Fuel surging?

It has only done it aabout 55mph. Tach guage went out the first time it has done it. It sounds like it revs up and comes back down on its own. Not real high but maybe 200 to 300 rpm and just bounces between 1500-1700 rpm. It will sit and idle all day and not have any issues.

I cant really explain the symptoms well. Its almost like im lettng off the throttle and tapping it. The cel came on but went off. I do have a delay in the wts light of about 15 seconds or so. Then i can hear the pump and then the light goes off. I havent had the throttle issue for about 2 days and the cel hasnt come back on. But when i shut the truck off at the store or something when i return i cant get it to start

I will try the crank shaft position sensor. Thank you

I have to let it sit for probably 20 min before it will start back up. But i did find out that if the truck is below running temp i can shut it off and start it right up