As far as I’m aware the cruise control on this model is literally just an actuator pulling on the throttle. It is unable to shift your transmission or do anything other than mimic your foot on the gas. This sounds more like a transmission issue.

 

Thanx, I'm looking into all of possible causes. Seems reasonable that it is transmission since I have had other trans issues and it's being rebuilt.

 

Have you had your codes read?

How steep is the hill, how high are the winds and what speed are you travelling. Watch to see what speed it's happening at and try setting the cruise control for 5 MPH lower than that speed. There is a good possibility that the speed you are trying to run at is close to a shift point. As the vehicle starts to slow down a little due to the resistance of the steep hill or the wind the transmission is told to drop down a gear to accelerate back up to speed. I've dealt with this issue while going up relatively large hills in a few different vehicles. 4 cylinders are especially susceptible to this due to their lack of power, but the gen1 X will also likely have this issue since it is under powered for it's weight even with the 6 cylinder.

If you try setting it lower and this doesn't remedy the situation then...

As Blackberry said, transmission, or possibly the Throttle Position Sensor. A bad TPS can also cause the transmission to do odd things as well, such as missed shifts etc.

Have you checked the transmission fluid?
This is done by warming up the vehicle and parking on a level spot. With the vehicle running pull the dipstick and check the level for the "hot" portion of the stick. I typically check it about 3 or 4 times to make sure I'm reading it correctly (no excess splash or residue from teh dipstick tube). It has to be done with the engine running and the vehicle in park.

 

Have you had your codes read?

How steep is the hill, how high are the winds and what speed are you travelling. Watch to see what speed it's happening at and try setting the cruise control for 5 MPH lower than that speed. There is a good possibility that the speed you are trying to run at is close to a shift point. As the vehicle starts to slow down a little due to the resistance of the steep hill or the wind the transmission is told to drop down a gear to accelerate back up to speed. I've dealt with this issue while going up relatively large hills in a few different vehicles. 4 cylinders are especially susceptible to this due to their lack of power, but the gen1 X will also likely have this issue since it is under powered for it's weight even with the 6 cylinder.

If you try setting it lower and this doesn't remedy the situation then...

As Blackberry said, transmission, or possibly the Throttle Position Sensor. A bad TPS can also cause the transmission to do odd things as well, such as missed shifts etc.

Have you checked the transmission fluid?
This is done by warming up the vehicle and parking on a level spot. With the vehicle running pull the dipstick and check the level for the "hot" portion of the stick. I typically check it about 3 or 4 times to make sure I'm reading it correctly (no excess splash or residue from teh dipstick tube). It has to be done with the engine running and the vehicle in park.

Thanx for suggestions, been doing a lot of trans work, just picked up a trans body to rebuild today. As raspberry suggests, probably a trans problem. Will check back in a week or so. A little busy trying to get the ECM repaired so I can get smogged.

 

Forgot to mention. If the trans fluid is low and you go up a steep hill the pick up tube in the pan can start sucking air as all the fluid sloshes to one end of the pan and cause the transmission to start slipping. This doesn't sound like yours because you said it's happening on flat ground with high winds, but just another reason to ensure the fluid is correct.