If its a TH350 then its probably not the original transmission. By '83 they had started using the 700R4 overdrive transmission. This means you also need to also look at the transfer case to see what you have.
The most likely model is the New Process NP208, which is a medium duty chain driven case. The best would be the gear driven NP205, but this would be uncommon even as a swap. They were only used on older trucks, and often only with a 4 speed manual. The chain driven full time NP203 is also a possibility, but it was also only stock on older trucks. You may want to look at this link to see the differences Tucson Off-Road Forum • View topic - Transfercase Identification----CHEVY TECH
Based on the lift I would also try driving it over some rough bumps to see how bad the bump steer is. They should have installed a dropped pitman arm (like this one Offroad Design - Steering Correction
) to keep the steering lined up with the axle, but some folks skip that step. It can make it very hard to keep on the road when you hit bumps.
Another place to check is where the steering box is bolted to the frame. With big tires this is a high stress area and the frame may begin to crack. You can weld on or bolt in a reinforcement for the frame (like this one ORD Chevy GM Steering Box Brace and Bolt-in Frame Repair
These trucks are relatively cheap to keep up because they are built like a tank, and most of the drivetrain parts are identical to what was used on cars. You can almost always find parts in the junkyard, or at a reasonable price from an auto parts store. Their weak point is body rust, especially the lower sections of the cab and fenders. If you run it hard you are also going to break things, but that's also the case with a newer truck.