Hi. I have a 2007 Equinox AWD. (not the sport). This week I noticed that the car is doing something weird when I accelerate up a hill. At first it happened in the rain and I thought the wheels were having a hard time gripping then it happened again on a dry road. It feels like the car can't grip the road and kind of slips BUT it doesn't shake or make noise or buck or jerk or slide. If I let off of the gas and then press it down again it starts acting normally. No warning lights have come on. I did have the ERG valve replaced within the last 6 months because of the constant stabilitrak light issue. Does anyone have any idea what is causing this weird behavior?

Thanks!

Edited to add: the truck has 127,000 miles on it. No previous issues except above-mentioned ERG valve.