Having problems towing, my Travel Trailer weighs almost 7000lbs. The truck is stock except for a 4" exhaust and I have not gages. On my way home from a trip the hills were really dogging it out and seems to be making a noise in the Turbo area at 65mph 1800-2000 rpms, off the hills it seems to be ok. Not burning any oil temp is normal. Any ideas? 1996 F350 7.3 PSD 4X4 LB CC XLT.