Sometimes when I press on the gas, the truck will begin to move forward slowly then I will feel a thump and the truck ends up moving much more like it should.

It does not happen all the time and happens from a complete dead stop. When I start off super slow it does not do this.

What do you think this could be?

 

Where does the "thump" feel like its coming from? Driveshaft u-joints maybe?

 

It feels like its coming from the rear.

 

transmission in need of service, fluid and filter change and bands adjustment, my mighty dodge does that when in need of band adjustment, well the last tree times that has worked for me