our 96 dodge 2500 5.9L 360 engine has been surging on and off for quite some time. it usually happens when the truck is warming up. this happened last night about five minutes after i started it while preparing to go out plowing. i have cleaned the throttle body a few times, and this seems to help temporarily, but ONLY temporarily. once the truck has run for more than an hour straight,the problem seems to disappear. any ideas, or thoughts?