03 envoy has 272000 miles, around 1500 rpms or 55 mph, rpms seems to want to drop down. when this happens it makes a humming sound? when i let off gas it stops. the vehicle is not towing.
It sounds like your low on fluid, or your transmission filter is dirty and the front pump is not getting enough oil supply. Worst is your front pump is going bad.
Check the fluid level and see if it's burnt. Good luck
When you get your new transmission, you could always have them so a simple up grade. If you have the same transmission as i do, the 4L60E. Have the transmission tech swap the servios with a corvette servo. It's a great up grade the part it self is under $25.00 and there is no internal parts to be changed. I had mine changed by the dealer before i picked up the Jimmy when i bought it new and now i am at 325,000 miles. Good luck http://s-series.org/component/option,com...
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thank u! most likely its the pump :( at around 67,000 we had the trany rebuilt and around 15,000 more it went again and had it totally replaced, so we check the fluid often. i pilot car oversize loads so its mostly highway miles. it also makes the sound when going slow (35 40mph) up an incline behind a large load.
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