Just trying to get some opinions here. 2016 Suburban, 139,000 miles. Truck has been running fine for the past year or so that I have owned it. I first started noticing a rough ride (its not really rough, just not smooth like it was) about a week ago. Almost feels like a cylinder is missing or something to that effect. I should mention, even to this point, there has never been a check engine light on. Then I started to notice a whistle or high pitch screeching noise when i would start the truck. It would last a second or two, then it stops. Put the truck in drive and start to accelerate and as i get the top end right before the transmission shifts, it screeches/whistles again until the shift is made and RPMS drop. When traveling on the highway, even on cruise control, i notice a little bounce on my tachometer...not much, but ever so little, which I hadnt seen before. I have not clue where to look? I took the mass air flow sensor out and gave that a good cleaning with Sensor Solvent I bought at Advanced Auto, but that made no change. Transmission itself is shifting smoothly. I know something has changed, but I need help here before i take it to the dealer. Any ideas?

 

Sounds like the serpentine belt tensioner has lost it's tension. Belt and tensioner kit would be in order. Rock Auto will have what you need.
At your mileage most likely the struts and shocks have worn out.