Is this a good used truck to buy

The truck will drive fine with only 4 gears. But, we don't know why it has only four gears. It could be a broken gear or something bent not causing it to go into gear. There may be some of that broken material in the gear box, which may find it's way into the rest of the gears. The good news is that it's not that hard to find a used transmission, and they're relatively easy to bolt up. The fact that you have 33's on it means you don't need 5th as much as you did with the smaller stock tires. But you will miss it on the highway and going down hills. That motor is good for 250K+ if you take care of it, and never drive it once it gets hot. They blow head gaskets when people don't realize theyre getting hot and keep driving them before fixing the problem. I love that truck and would buy it in that condition, if the price is right mind you. If you brought me the new gear box, I would have in in in a few hours tops. So it won't break the bank if it does go for good. What are you planning to spend on it, is it inspected? How are the other important things like brakes? Also, if you get it, find out if it has synthetic oil in it. If it does, you should use it, but if it doesn't, do not put synthetic oil in it! These old motors do not take kindly to it, and you will blow engine seals.

10W30 in the winter, 10W40 in the summer. I like Castrol GTX for the price and the performance. Remember, NO synthetic unless it's already in it, you will blow oil seals if you do.