Thought I'd follow up on my last post. This problem seems to have fixed itself. I now think I filled up with a load or two of crappy gas. I do now notice some very minor pinging but I would think our local fuel suppliers are still pumping the lower BTU winter grade fuels.

Thanks for those who tried to help.

Minor pinging shouldn't hurt, but I still don't like it. You COULD retard the spark by 0.25 degrees, which would probably get rid of it (and shouldn't cost you much in power). I wonder if you're running slightly lean? That can cause pinging too.

- Jack

I don't like that it fixed itself?
Now there is pinging?
Could have been bad gas but maybe check the fuel filter?
Could have gotten water from the station.
Try the timing as Jack posted earlier. Keep us posted.

Lars

Slip Yoke
 

Does this happen on take off from a stop or will it do it when accelerating while already under motion? If it does it on take off what you explain sounds like the slip yoke on your driveshaft binding on the spline and then freeing up, that gives you the kick in the but that feels like something hitting the tailgate. Pull the driveshaft and feel inside the slip yoke, is it rusty? If is feels real sharp on edges of spline it may be worn and binding causing wiindup in drive line tahe it lets loose and bangs. T see if this is the issue pack the spline with a good grease and reinstall shaft in truck and try it out. If it has a 2 piece driveshaft lube both splines. Good luck JF

I had a miss I guess you could say. i added +10 for WOT fuel and it has went away and my truck seems to run so much better. I do have a aftermarket intake though.