Maybe a transmission problem?

There could be several issues that could cause your GMC Envoy's transmission to not shift gears properly and the RPMs to rev high. Here are a few potential problems that you may want to consider:

1. Low transmission fluid: If the transmission fluid is low, it could cause problems with the shifting mechanism. You'll want to check the transmission fluid level and add more if needed.
2. Faulty shift solenoid: The shift solenoid is responsible for directing transmission fluid to the appropriate gear. If the solenoid is faulty, it could cause shifting problems.
3. Worn transmission bands or gears: If the transmission bands or gears are worn, it could cause the transmission to not shift properly and the RPMs to rev high.
4. Clogged transmission filter: A clogged transmission filter can restrict the flow of transmission fluid, causing shifting issues.
5. Faulty transmission control module (TCM): The TCM is responsible for controlling the transmission. If it's not functioning properly, it could cause shifting problems.

I would recommend having a mechanic diagnose and fix the problem for you. It's important to address transmission issues promptly, as they can lead to further damage if left unchecked.

The shift solenoids may not be getting the correct signals from the transmission control module . Read the codes to see if it's the solenoids or the module.

could beTPS sensor[RPM] maybe need to be replace.is in throttle body[gas line]

run the fault codes to determine the fault are a first
next check the vacuum hose for the transmission actuator as that unit has a lot to do with shifting ratios

Your transmission is probably jumping in and out of "torque converter lockup". The lockup is the most efficient mode because 100% of the power from the engine goes to the wheels and is not lost in the torque converter. It only goes into lockup at higher speeds, but will jump out if the computer senses it needs more power (at the higher engine RPMs) to maintain or increase your speed. I recommend either going faster or slower if this is bothering you. :-)

You may have low vacuum pressure which can screw up the fuel regulator as well as shift points. I would start by checking for vacuum at idle, and if low, check for a disconnected, broken or kinked hose.

Check the output sensor on the transmission,
With out a speedometer the transmission does not know how fast you are going or when it should shift

With normal acceleration the 1st to second shift point should be around 2500-3000 rpm. Most of your shifts under moderate acceleration will take place at this same point or when there a light load on the transmission. Under hard acceleration the RPMs will climp higher due to increased power needs and the computer will shift when less power is needed or the RPMs climb to an unsafe speed say5000-6000rpms (depending on where yours redlines). Also going up a steep hill will raise the RPMs higher and goind down a hill will cause a faster shift at lower RPMs. These can always be altered by an individual owner by adjusting shift points, using performance parts and if you have problems (low tranny fluid/trans issues). Your trans RPMS are fine and will vary depening on how your foot accelerates. The shift pattern should be the same every time you drive slow/medium/fast/, look for changes in those patterns you will also catch a problem early.

If you're only in "D", you should switch to "OD" when driving at higher speeds. "D" only allows you to move up to third gear whereas "OD" will move you into fourth. You're over-working your transmission by driving in "D".

maybe the speed sensor on the transmission monitors transmission speed and sends info to computer to control shifting not sure if this is helpful