I have a 2000 Chevrolet Tahoe 5.3, 4l60e transmission. 4wd. This is the 3rd transmission that this truck has burnt up 3&4 gears. Went with a aftermarket cooler on the 1st one, and it burnt 3-4 up. Next time around I went with aftermarket cooler with electric fan. ( thermostat range was 165°-180°) Steel braided lines, aluminum pan. Had the ecm reflashed to stock. Transmission oil Temperature gauge inside. New dipstick tube, (yes it was the same length) new shifter Cable, new park neutral Safety Switch. Full synthetic ac delco transmission fluid, new torque converter, yet it has lost 3rd & 4th gears again. Truck has not been driven hard, fluid level has been checked religiously. Why does it keep burning up transmissions? All have been btwn 3-5k when it happens. Except for this one. Has maybe 2k on it. Guy says it could be because of having 20" wheels on it? Really? Or the mass air flow sensor? I'm stumped
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same builder for all of the transmissions? what size are the braided lines?

 

I would change builders. performabuilt comes to mind if you don't want to blow the bank on a good build.