Had my truck in the shop for overheating and I told the tech that it was also having problems shifting at around 25 to 30 mph. If I maintain that speed, it shifts up and down continuosly. The tech's simple answer was "turn the overdrive off." How profound!! I've had 3 F150's with the same engine and tranny in them and none of them have ever done this. I've had 8 automatic vehicles in my life and none of them have had a problem like this in that I have to take the OD off to just drive at lower speeds. Can some of you other owners out there try driving at 25 to 30 with the OD button on and see if you experience the same problems. If it matters, I have the 3.73 limtied slip rear end.

 

the EEC SHOULD hold 3rd until 45mph, typically. I have a 'bird with 3.73s, the 4R70W has the same ratios as your 4R75E(W). Tell the tech at the stealership to reflash the EEC. The brain is most likely the problem if the trans doesnt have any physical problems. Also, a good SCT tuner can and will tweak your shift schedule to hold 3rd at 45mph and will specifically write code for it if you ask. Constant 3-4-3 shifting is painful on the trans, as is 4-2 shifting as excess pressure is placed on the OD band.

 

Had a chevy with a bad rebuilt that did the same thing. Toasted the trans in less than a year. Glad you know a BS answer when you hear one, take your truck somewhere else if your tech is too lazy to offer a real fix. This is a 08 and should work perfectly or you should get a loaner untill it does.