98 Sonoma 2.2 automatic tranny issues.

Good morning! I spent a couple hours last night reading through several posts looking for a problem that was like mine so I didn't need to ask a redundant question. I found a couple that seemed like mine, but not being a wrench spinner or "mechanical guy" made it a little more difficult to know exactly what I was reading about. I'll just describe my problem and ask for any advise or assistance you guys have. Know this, I'm not going to do any work myself...I just want to be armed with a little more information when I try to find an honest tranny shop. I stopped by a few "reputable" shops yesterday and both of them quickly mentioned a few fix ideas then focused heavily on rebuilding the tranny. From what I've read in posts here, it seems more like an electrical problem, valve thingy, or silenoid whatchamacallit stuff. Again, I'm in no way a mechanic...just looking for guidance prior to seeking the right man to do the work.

Here it is:

98 GMC Sonoma, engine runs great, 2.2, automatic, fluid red and not burnt, no engine service lights, serviced tranny bout 8000 miles back, about 130000 miles, absolutely no other issues with the truck...now the problem...when i put it in D or 3, it's just sits there like it's in neutral. I can put it in 1 or two and it will take off fine. I can shift from 1 to 2 then can get 3 and D manually if it already moving. Once in 3 or D it will do fine unless it has to down shift. I can manually shift through all the gear manually and even took it on the highway and drove about 20 miles in D and it was just fine. No noises like anything is wrong. I read another post very similar to mine and the guy put another tranny in his jimmy and still had the same problem. A lot of you guys advised it was electrical or something else and thats why I feel like I need to be armed with more information prior to talking to a tranny guy who will just talk over my head.

Anyone with knowledge of this type of problem and would give me information would be greatly appreciated.

I don't want to complicate the trouble shooting, but here is what I believe to be another unusual issue. If i drive it in overdrive for a couple miles at 60 to 70 mph (there abouts) and the get off the highway and stop, get this, it will work fine for a little bit. I mean it will actually shift fine. It will engage in drive and shift just fine throught all the gears up and down automatically. Eventually it will act up again and have to shift manually. Ant info would be appreciated. Love the truck and I'm pretty sure after reading some other posta that I don't need a new tranny. Thanks in advance for your help.