my dads 2000 3500 in the last month has started these surges on and off droping 100-150 rpm, its got 148000 ml does something need ajusted or what?

 

Check lift pump pressure immediatelly. Replace lift pump if below 5 PSI. Get ready to replace VP44 in near future in all probability. Check for codes by cycling ign key on three times. Read in odometer and report.

 

thanks for your help. the code said p-done, so if you know what that is please tell, thanks

 

Go to ORilley's & use their scanner. Codes don't always show with the key. Autozone & Advance also loan scanners but theirs wouldn't reset codes last time I checked. Do you have gauges?

 

It is possible your IAT sensor is dirty or failing. The grid heaters draw enough current to affectr the tach reading when they cycle.