i have a 92 w250 i just had the injection pump replaced and i have been driving it for a while with no problem. i just took it on a long trip and the trasmission would drop out of overdrive into the lower gear as soon as i let off the gas. i get back into it and it shifts back in to overdrive. i don't want to hurt my trans more then it is so if anyone could help me it would be great.

 

Sounds like the TPS is misadjusted or bad. Take a look at the sticky in the 1st gen forum for adjustment directions.