no idle or shifting.

I have a '97 Ram Van 2500 wihh the 3.9 V6. It sits for months at a time between uses. I recently took it out and noticed it was very slow to shift into 3rd. Soon it would never shift into thrird. Then it seemed to stop downshifting to first when I came to a stop (fluid levels are good, no burn't smell). So one day I put it into reverse to back out of the drive way, and it dies. I had to give quite a bit of gas to get it to start, and it would NOT idle without my foot on the gas pedal. What do you think, did the tranny go out and take the torque converter with it, or is it something simple like a throttle position sensor? Anyone else had a similar problem?