I own a 99 Suburban 2wd with 113,000 miles. When I tow even the smallest trailer I get a bad shudder in the front end and it feels like it is losing power going up hill. I have bought new tires and it still shudders. I have been told it may be the Torque Converter. It occurs in O/D or 3rd gear. The owners manual says tow in O/D. The vehicle does not shudder without trailer. I bought the vehicle when it was 1 year old and it has had a short whine noise from the rear end at approx. 30 and 50 mph under strain with or without a trailer. I added a small bottle of fluid at the advise of a mechanic ( The name escapes me)made by Ford into the transmission. The truck started skipping very bad and I had to get the transmission flushed, The skipping stopped and I'm back to my old problem. One time towing a small boat uphill it shudderd and the check engine light came on and went out. The code is p0430, with light off now. I believe all of this is related. Help Please!