This is not a normal operation. It can do it like 10 times in a row for no reason. I could see it do it once but not several times in and out, in and out.

 

My fix on the '97 'Burb was the 4.10 gear install. It came with 3.42 gears. Now I can climb hills and accelerate from 45 to 55 mph without TC unlocking or downshifting out of OD. Before gear change, almost any change in accelerator would cause TC to unlock, now you really have to give it the go juice to unlock. I gave up 1 mpg, but man does it drive better. RPM's increased from 1500 to 1850 at 55 mph. Towing MPG went from 7 to 10. Savings on 6k mile trip towing camper paid for gear change.

If you suddenly or over a period of time notice a change in TC operation, start looking at engine. Could be time for a complete tune-up and filter change. Anything that will cause a slight loss in power will cause TC to act different. The TC lockup is directly related to speed, throttle position and strain on engine. Even a change in what is inside vehicle can cause TC to act different.

 

Ok....so I was having a similar problem, and this might not be your problem. I have an 04 GMC Yukon Denali Xl 1500 6.0 AWD, problem began very randomly at highway speeds 50+. It felt as if the transmission was shifting out of gear for a second then back in. As I drove farther it became more frequent. No check light was on...felt as is I was losing power for a moment. I would shift down to 3rd and it seemed have the problem less frequent. But as I drove in 3rd it began happening more often. Oil pressure gauge was a little higher than normal...around 60, usually 40-45ish. Nothing to be worried about. I did notice the water temp gauge fluctuating out of normal. Would go down to 180 back up to 210, down to 160 and that is when I had the lurch. Looked all over for a solution....MAF sensor....transmission sensors....nothing, at least no one was posting. Replaced MAF sensor with no change. Found one article that talked about the Engine Coolant Temperature Sensor that said a malfunctioning ECT can cause the engine to change fuel mix based on coolant temp. At cold it produces one mix at higher temps another mix. With the fluctuating gauge I thought what do I have to lose by changing it...about $25. Replaced it, was easy to locate and remove with only a small amount of coolant lost. And Bob's your uncle....it fixed it and ran again like normal. This may or may not be your situation but I thought I should post since there hasn't been very many solutions posted. Good luck.