Transmission problem
1997 Oldsmobile Bravada 6 cyl All Wheel Drive Automatic 137000 miles

Hello, my check engine light recently came on in my truck. At first I didn't notice anything, then the light went off. About a week later it came back on and when my boyfriend put it into drive and went to move he hit the gas the engine revved but the truck hesitated. He put it back into park and then into drive again and it went with no problem. I got in to drive it yesterday and right away it seemed to be slipping from stop to first gear. I went to advance to get some stop-slip and it did not seem to have any effect on the problem. Today I got into the truck and the check engine light is still on but the truck ran just fine. Could this mean that the solenoid is bad? I thought that if it was the transmission itself the problem would be continuous not intermittent. Please help me if you can. I do not want to take it to a garage without knowing a little about this as I feel it would be very easy for them to take me to the cleaners and say that I need a new transmission. Any help would be greatly appreciated.