how hard is it on our trucks, what is involved, and does the motor have to come out?

 

The rear main seal is not an easy replacement. Either the engine has to come out, or the transmission and adaptor housing removed and the rig up high enough to reach the back of the engine and still be able to block up the front of the engine to get the oil pan off. The flywheel has to come off, the oil pan removed, and then there is a plate with six bolts on the rear of the engine block with the seal.

Frankly, it is much easier to pull the engine than not.

 

Rear main seal? That being the crankshaft rear seal, the oil pan does NOT have to be removed just the flywheel.