Nola said:
I wonder if this is strings or the pickups...I know the MIM don't have the best pickups, but not sure if it's worth sinking $70 into upgrading them when the sound is like 90% where I want it.
Pickups are subjective. I'm not a p bass guy but I find MIM Jazz pickups sound pretty decent. Once you start swapping pickups there are a lot of choices depending on what sound you want. Research is important to get it right. Also some MIM basses are very good feeling and playing instruments - could be a deciding factor on whether or not it's worth playing with the electronics.
Strings make a huge difference as well. I'm not sure if you've mentioned what strings you're using currently. A few people have already mentioned flats. "P-bass" and "flats" are a very popular combination in recorded music. As with pickups there's a huge number of choices available depending on what kind of feel and sound you're going for.
Hex core strings have higher playing tension than round core strings. Hex core is more common. Comes down to what you prefer for feel. Trying different gages can make a difference as well. The bass will tell you what it likes if you experiment. String to string balance can be affected by doing a proper setup and adjusting pickup height accordingly, along with the type and gage of strings.
Nickel on steel roundwound: The most common strings. Nothing special really, but useable for going after specific tones. They sound bright and piano-ish when new. The zing factor tames a lot as they break in fairly quickly. They sound subtle and non-agressive when broken in with decent midrange. With any type of string, if the tuner bobbles and can't find the note you're past due to change them. They can tend to sound "mellow" or "dead" fairly easily.
Stainless Steel rounds: Harder on fret wear & fingers. More agressive sound. Brighter. Mid-scooped. Popular for slap. Marcus Miller. John Entwistle.
Pure nickel rounds: Less common. Nickel alloy rather than nickel plated steel. Mellow sound.
Coated/treated strings, eg. Blue Steels, Elixir, some of the DR offerings etc.:
Run of the mill roundwound strings have a useful lifespan before they need to be changed. In general, all strings will lose some high end as they age. Coated strings can be slightly more expensive but claim longer lifespan. If a player sweats a lot and has acidic sweat, these guys have the ability to kill fresh strings in a matter of hours. Coated strings can help to counteract this. They're not all the same. They won't have the zing factor of fresh uncoated rounds. Some of them sound dead on arrival.
Experimenting with bass strings can become expensive.
Flats:
Tons of options for flats. They tend to be moderately to extremely more expensive. Guys who find the flats they like tend to leave them on forever or until they break, whichever comes first. Purportedly, Entwhistle would change his strings daily. Flat guys often talk about their 8 year old strings. Wipe them off to clean.
Flats also tend to have less harmonic overtones and bigger, more powerful fundamentals. Difficult to impossible to find flats that have the zing factor of fresh rounds. They can sit in a mix beautifully. They reduce string noise and fret buzz a lot. A metric tonne of 60's music is the sound of flats, very often on a p-bass. Motown, Wrecking Crew, Beatles, Iron Maiden etc. Flats.
Monel, Nylon, Tapewound: Haven't had a chance to play on these ones much. Wouldn't expect much response above 100Hz or so. Might be a good choice for dubby & tubby.
LaBella: They have a few different options. One is the Jamerson set. The Deep Talkin' series gives you an idea where these things go tone-wise. Boom. Thud. Try them with a pick.
D'Addario Chromes: Tons of deep bass. Plenty of high end. Almost zingy a bit like a stainless round but not quite. High tension. Mid scooped. Popular.
Pyramid: Beatles
Thomastik Infeld Jazz Flats: Check out the price of these things. Unlike any other string. Round core. Very low tension. A lot of players have a hard time with the feel of these things. Others love them for their ease of playability. They sound most powerful when you're not digging in too hard, so it takes a bit of time to find the right touch. Quite bright sounding when new but this will drop off as they break in over a few months. They don't have the huge low end of other flats, but that's not to say it can't be dialed in through your rig. What they do have which makes them unique is a very strong and clear midrange. They can cut through a mix with punch and authority. Also very responsive to eq if lots of mid burp isn't your thing. They sound great out of the package. A lot of guys will say they sound better as they age.
Precision Flats: Marketing ploy aimed at the popularity of a p-bass with flats.
As with rounds, different types of flats give you tonal possibilities that are all over the map. Flats can work great in just about any context if you have the right match for your needs. Some of them can be slapped, but this is where rounds have a distinct sound not quite possible with flats. I don't think you're ever going to get a zingy, buzzy Entwhistle sound from any flat but some are very different than others tonally.
Pressurewound strings: A few companies are doing this now. GHS and DR come to mind. It's a roundwound string that gets slightly flattened in the winding process. The feel is supposed to tend towards a flat while the sound is more like a round. Supposedly long life too.
tl;dr:
Strings and pickups can make a difference. Flats might be a good choice if you don't slap or like to change strings. When deciding what kind of tone you want, different string and pickup combinations can vary a lot in terms of whether the tone is mid scooped for dubby sound with immense size, mid-forward for cutting through a mix easily without killing everything, neutral, boomy, zingy, sharp, mellow. Some setups will paint you into a corner more than others, eg. good luck pushing the midrange up if it's not there to begin with. A lot of it is subjective and comes down to what you like. Once you find one of the various flavors of "good", you'll possibly find that it works in a wide range of context.
If it were me, I'd try to find the right strings and set the bass up properly for them before thinking about pickups.