Crusing at 1800 rpm, the tach needle is bouncing/ jumping up to 2000 rpm. And when this happens the truck seems to be bucking and jerking slightly. Any ideas??

Any error codes? 

 

Might fill out your signature so we know what year of truck and modifications you've got. Just of the top of my head sounds like a crank sensor but I don't know what year of truck your running.

99 2wd 3500, auto. Pretty much stock with exu and a air filter.  

More than likely the crank sensor like @Mopar1973Man says. Get the codes read to be sure. Hate to see you throw a part it.

4 minutes ago, dripley said:

More than likely the crank sensor like @Mopar1973Man says. Get the codes read to be sure. Hate to see you throw a part it.

 

Exactly! 

I scanned it, no codes yet

What did you scan with?

Hmmm... Is this an automatic or manual transmission?

It is a auto truck. I scanned it with a OTC Encore scan tool. It happens most at a small part throttle condition, i can barely feel it driving on the highway, but when i tow my trailor it becomes more noticable. If i give a little more throttle it goes away

Test for excessive AC noise issues. 

Then if you do find an issue, you'll need to replace your alternator then also consider doing this mod too.

 

 

I did the mod @Mopar1973Man mentions and my ac voltage dropped fron .035 to .010. I have only heard from one other that has done this, @IBMobile, and he did not see as much as I did but could not remember what his drop was. It will be interesting to see how this works out for others that chose to do it. 

I'm going to aim for doing this mod soon myself and see what happens too. 

I did the mod as well but put a new alternator on at the same time, so technically mine doesn’t count. I would check all of your wires as this could also be as simple as a wiring issue. 

Edited May 10, 20186 yr by Red Rambler