Ya I was running a 16 valve with a four to one x-fer case with 30x9.5 tires, pulled in the scales just starting off on the nine day camping trip the rig and the trailer weighed in at 4000 lbs  the trailer by its self weighed 950 with about 50 lb tounge weight, it still had plenty of more power to go faster but why push it ? that was with an inch and seven eights exhaust pipe, I got home and put a two inch pipe on it now it has ever more power.It did real well on gas mileage also I went from klamath falls oregon to lake view over the mountains and it took 3.8 gal of gas. just did the math 28.4 mpg. p.s. the trailer I was pulling is a 1951 m100 that goes with my m38a1 (looks like a cj-5)about 500 lbs empty.