i have a 96 ram 4x4 with 318 v-8 and auto trans. while im driving if i let my foot off the gas to slow a little bit the rpms shaply drop by 500 then jump back to normal and it does it only then but every 3 or 4 seconds during that slow down. never dies and idles fine. any ideas?????

 

does it jolt like the transmission is slipping between gears or is it smooth?

 

could be the IAC. you could try running a bottle of lucas trans fix and see if that affects the problem in a positive way. mine started doing that, and it was my o2 sensor that turned out to be the problem afterall, but i let it ride like that for a couple weeks before it got ridiculous. try cleaning the pre-cat o2 sensor and cleaning some gunk off of your IAC to see if that affects the surge your describing.

seems to me a bunch of people are having similiar issues with their trucks lately.