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Discussion Starter · #1 · (Edited)
just bought an 03 suburban 2500 from Travis @ csk 3weeks ago..it has an 03 lb7/Allison 5speed...while the engine seems to run good (injectors were done @60k...present @ 120k). One of the problems I'm experiencing is while cruising in 5th gear @ 65+ and accelerate to speed up the trans will kick down hard and slam into 4th gear and stay there until I shut truck off and restart. It won't go into reverse or any other gear, except 4th until I turn it completely off for a minute and restart. I only have this problem at highway speeds in 5th gear...I can mash the pedal through all the other gears and shifts ok until 5th. Also, it seems to have a slight hiccup/mis at highway speeds, esp. when slightly accelerating. I don't have any check engine light because for some reason Travis didn't hook it up or hook it up correctly. Idk..maybe transfer case?? Any help would be greatly appreciated. FYI truck has outlook monitor and triple dog programmer. Thx
 

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sounds to me like the trans is going into limp mode, would be easy to diagnose if you had a CEL. Anyway to scan the codes?
 

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Discussion Starter · #3 ·
I don't have a tech ll or efi live...but I'm pretty sure if one of the them were plugged into the obd2 port it would read the codes stored/active. I wish I knew someone in the Vegas area with an efi live or tech ll to scan my rig... I guess I'll have to go to gm dealer and pay the standard 1 hr charge for a diagnosis on it.
 

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Discussion Starter · #4 ·
Shift solenoid, maybe?
 

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I had an 03 duramax with the same problem. Never looked into it. Sold the truck. Had the solenoid replaced and still slammes into 4th when heavily accelerating.
 
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