All very interesting on the upshift problem but can anyone help me with my '91 350SDL in REVERSE? It lags when I shift into reverse and unless I wait a few seconds and apply gas
slowly, it jerks and screeches backwards. It has 129K miles and last month just had trans
filter and fluid changed after about 60K miles--know it's a little late. 2 mechanics tell me that
the trans is going and will require a rebuild. I'm getting estimates from $6K to $2.5K. Any
advice?

 

Swap into manual. Cheaper. $$$$

 

Don't think so. This is a '91 350 SDL.