I have a 1999 two wheel drive Tahoe. It has a towing package and fingertip steering, its loaded. I have had the allignment checked by four garages. Everything checks out great, no problems, I put on new tires, brakes, greased bearings,new rearend,new shocks. I can not tow anything over 60 miles per hour , 3000# trailer or a 500# trailer. If I go faster than 60 I start weaving all over the road. Truck had 55k when purchased, now 120k. Any thoughts?