Grand cherokee 5.2L 8cyl shutter problem

Hi, My friend owns a grand cherokee with the 5.2L 8cyl engine in it. I'm not sure what year it is but its not new I'm guessing maybe 95 or 96. He has about 169,000k miles on it. I'm going to explain the problem as best as I can. My friend explained it to me. He said when hes going up a hill going about 40mph the jeep shutters. He thought it was the transmission so he brought it to cottman transmission and they said there is nonthing wrong with the transmission. They said something is wrong with the motor, they didnt know what, but they blamed it on the motor. I thought it was the torque converter but cottman said nonthing was wrong with it..ok. So now I'm guessing maybe motor mounts, maybe it could use a tune up(spark plugs, cap and rotor and wires). I dont know alot about engine diagonistics so I wanna hear your opions before I go ahead and replace stuff. Thanks guys! You guys always pull through. Later, Ty.