Wondering if torque converter isn't locking up

Wow, Techntrek, you have been busy investigating! There could be several coolers in front of the radiator: A/C condenser, transmission oil cooler, power steering fluid cooler (similar design, but smaller), and in some rare cases an engine oil cooler.

It all sounds much like a typical towing situation, except in this specific case, temps and fuel consumption have suddenly changed without external changes (such as adding weight or wind resistance), indicating a mechanical problem. What is really unusual is that the situation does not seem to be getting worse.   

The fuel mileage, of course, can be effected by the lockup converter's performance, but the transmission temperature rise while in tow/haul wouldn't be effected by the lockup converter not operating. Because the lockup converter is disabled in that mode, converter lockup failure would not be the cause of the temperature rise (over the normal towing temperature) while towing.
A few fractured vanes in the converter could explain both of these variations, higher transmission oil heat and lower fuel mileage under all conditions, but usually you would feel a vibration from the "out of balance" condition of the converter, also you should notice some "compromised" performance in daily driving.

From several hundred miles away I would never "hang my hat" on such an unusual diagnosis, it sounds too much like more than one problem. At this point I would try one of the many automatic transmission shops that offer a "free" checkup. One of the dilemmas with buying an expensive scanner is it may not find the problem and even if it does, "you are still in, 'What do I do with it now?' territory". Unless you have a shop, access to parts, and the skill to make the repair, you are still stuck with having a transmission repair shop make them. The bad part of most automatic transmission repairs are they are usually made internally, meaning removal and disassembly, which is labor intensive, therefore, expensive. Good luck and keep us advised.

Originally posted by techntrek onfirmed lockup or not, it sounds like a professional checkup is in my future... once I find out if I'm furloughed as of Tuesday... or maybe on the 17th... or maybe again in mid-November.

Are you a Federal Employee?  I faced many years with a similar uncertainty at the end of our Fiscal Years.

Bob

Well Techntrek, you may be right about your Chevrolet. If that's true, the increase in "slippage" without the lockup could explain the extra heat.
Most of my experience has been on my own Ford products and damage incurred to a torque converter towing in overdrive. I was told the torque converter's clutch wasn't strong enough for even a 3.0 V6. According to the techs at the dealer, my Jeep does not lock up in the tow haul mode, and stays in 5th gear.