Look at the 8th digit in the VIN number to determine which engine you have. There are two engines, W and X. W is by far the most common. It is a 4.3L, 262 cubic inch V6 with Central Sequential Fuel Injection (CSFI). Obviously you have read through some of the other threads, so you know what needs to be done for a complete tune-up. Another suggestion to help with the rough idle is to add a bottle of Techron to your fuel. Techron seems to be the best at cleaning the injectors and poppit valves.
As for your tranny problem...bad news. Of all the common tranny problems it sounds like you have one of the few that requires rebuilding or replacing the tranny. It sounds as though you have a broken reaction sun shell. This problem is fairly common. The shell is weakened as a result of shifting between reverse and drive without coming to a complete stop. The symptoms are loss of reverse, second and fourth gear. I'm guessing that on your way home, it actually shifted in 3rd at 3,000 RPMs and you assumed the 2-3 shift was okay because you didn't feel it.
