I know its a 2.8l v6 I believe its the LB6, looking for some cheap and simple performance upgrades. I've heard you can swap the throttle body from a 3.3 into it? Sway bars? I know it shared with

Did you swap out throttle bodies? You may need to replace the PCM if you did. I don't think there's a way to rechip but then again maybe...

the used one is bad too--cud be a number of things from electrics to mechanical----------make sure the proper fluid and level is rite--is the ajustment correct at the throttle/accelerator--torque convertor cud hav issues-does truck stall--valve body and solenoids cud be dirty--get a haynes manual or othr repair book-or bring it to and honest trans guy fora testdrive

Will it start on starting fluid sprayed into the throttle body ?
Have you checked base fuel pressure at the injectors ?

check the pcv valve as they will gum up if the oil has not been changed regularly. I would also check all vacuum hoses for cracks or breaks

sounds like throttle body not fitted correctly or needs adjustment of idle sensor or idle speed control

Check the Mass Air Flow Sensor, you can get a can of cleaner specific for cleaning them for a couple bucks at the parts store. I'd just get 1 and clean the sensor see if that works. The MAF sensor is either in the throttle body itself (bolted on from the outside or in the air line between the filter and throttle body. That could be the whole problem right there. Good luck.

did u look at the coverter or pick up coil

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What is the fuel pressure reading now? Has the distributor ignition rotor ever been replaced? They burn through and cause all kinds of problems. Also this could be spark plug wires leaking or shorting out to the engine block. I would take a very close look at the ignition systems condition.

This is a simple job so don't get scared and you can do this yourseld with some cleaner a rag and a small brush, just remove everything around the throttle body and you can go to your local auto parts store and buy a cleaning kit for about $5. If the deposits are not too thick and have not cooked or burnt onto the plate or throttle body, you should not need to remove the whole throttle plate assembly. With the engine off, simply remove the air hose from the throttle body intake and carefully wipe away the deposits from the perimeter of the throttle body and the throttle disk. You can manually operate the throttle while you are doing this.

This is a simple service that I've never seen mentioned in any owner's manual and I'm sure a great number of people pay for unneeded misdiagnosed repairs when all that is required is this simple cleaning. It does make a difference. You should do this at least once a year.
The '99s and up have an electronic TB which as you've read are prone to failure. Cleaning is still recommended and sometimes necessary when idle becomes erratic or if you recently had a MAF or 02 sensor go on you and it might be gummed up. The volvo intake is "dirty" anyway so after a while it will always have to be cleaned.
To properly clean the ETM on a 99+ turbo Volvo you need to remove the TB and clean it on a bench. Its tucked way under the intake manifold and its impossible to see what you're doing without removing it. Also replace the gasket.