I recently bought a 2007 Suburban 1500 with the 5.3L. I also have a 24' enclosed trailer that I need to pull with it. Everything in the spec sheets says this should be no problem. However when I began pulling with it I noticed that at 70 miles an hour my suburban will not shift out of 3rd gear, which runs my RPM's at 3000 plus the whole time. I have also noticed that when not pulling my truck lurches when at mid throttle which is indicative of a torque converter failing. would an aftermarket torque converter purchase solve both of my issues allowing my transmission to change to drive when towing my trailer?

 

Welcome to the forum.

Have you switched it into the tow/haul mode?

 

I used tow mode and also switched out of tow mode to see if it would change gears on the highway. It stayed the same.

 

Seems like trying to pull such a large trailer at such a high speed is asking a bit much of your truck.

 

I towed for thousands of miles pulling 5000+ lb trailers all over the country in third gear, with the engine spinning at 3100-3200 RPM. Had the 4.10 axles. That truck now has 240k miles on it, with the original engine and transmission.

And yes, 70 is probably too fast, seeing as how most trailer tires are rated to 65 MPH max.