I put amsoil sae75w-90 with the proper amount of mopar friction modifier. I only towed a small 2 place trailer for about 2000 of the 7500 miles. I keep the speed under 115kms/hr when towing. The problem is i get chatter everytime i make a corner on pavement while applying throttle, kinda hard not to do. Today i changed over to the series 2000 amsoil75w-90. I took it for a 3 hour test drive and no chatter at all, and that is with no friction modifier. I talked to the amsoil tech line and from what information i could pry out of him i found out that the series 2000 has more friction modifier in it. If i had to do it over again i would go right to the series2000 and skip the regular sae75w-90. Has anyone else had similar results, or should i say problems.