Check engine light on, code B2600

Okay, was going by the original post saying it was the same as the 90 which has EGR. No problem, my fault for not asking earlier. Doesn't make much difference with the problem though. If you have the old distributor handy you could check the advance unit. You strip the distributor down; remove the crank senor plate and you will see the advance unit under it. Basically, a couple weights and springs. It can come apart and clean off any rust/dirt or crud, give it a couple drops of oil and make sure the weights move freely, I have seen some develop a ridge from wear and then they will catch just enough that the weights don't move free. Attached is an image of those solenoids. The EVAP purge on top can cause you issues if it was stuck open, the truck would be hard to start because the extra fuel vapor from the canister would make it act like it was flooded all the time. The PRC solenoid controls vacuum to the fuel pressure regulator if it was stuck open the regulator wouldn't increase the fuel pressure at higher rpm, but you only have the mid rpm bobble so it's likely not the problem as you would have a loss of power at higher rpm if the pressure was low.
The Lock and Free solenoids are for the differential and 4X4 system.

Great to hear, Sort of strange though unless it was leaking into the line? Usually, they will cause power to drop off at the top end.