1996 2 door GMC Yukon cruise control quit working

In 1970 I bought one of the first Chevrolet Blazers. I drove it until two years ago when it finally was just too worn out to drive, at close to 300K miles. I sold it to someone who is in the process of restoring it for show. I knew that I wanted an other 2 door Blazer, but they quit making them in 1995. After a long search I purchased an original 86K miles on a 2 door 1996 GMC Yukon SLE. I love this car.
However, I have just experienced my first mechanical failure. I am a fairly good shade tree mechanic. At 70 years old I have worked on every vehicle I have ever owned. So I am trying to figure out what has gone wrong with the cruise control. I live on the South Central Nebraska and Kansas border. On a return trip from our lake house in Kansas (yes, there are lakes in Kansas) to my home in Nebraska, as I was going up and down the rolling prairie hills, the cruise control started having trouble going up the inclines. Then it quit working altogether. I checked the fuses and they are ok. My next thought is the control unit has quit working. I looked for a replacement unit and saw the price… OUCH.
Is there something else that I could check before I replace the control unit? Is there any way that I can verify the control unit is at fault?
Thank you for any advice you can give me. I appreciate any help that I can get.

The first thing to check is if there are any brake lights that aren’t functioning. If there’s a brake light out the cruise control won’t work.

If the brake lights are okay, then take the vehicle for a cruise and then place the toe of your left shoe behind the brake pedal and pull up on the brake pedal. Now try engaging the cruise control. If it works the brake pedal switch is either defective or out of adjustment.

Tester