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Discussion Starter · #1 ·
I haul a very heavy truck camper and the truck does fine until I have to pull some grade . If Im runnin 65 mph at the base of the hill she'll slow down to 50mph but even with my foot mashed to the floor she wont downshift . All this time the speed and rpms are dropping while exhaust , engine temps and boost go through the roof !

Soooo my questions are why doesnt it downshift , is it safe to manually downshift it ,( if rpms allow ) is there a trans controller out there that I could use when loaded , or can it be reprogrammed ?
 

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I will downshift mine manually sometimes but most of the time it downshifts on its own. I had a old suburban and I used to manually downshift it all the time. That had a 700R4 and I got 160K miles out of it. And I towed about 6000 lbs with it.
 

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If its not shifting out of overdrive down to third at 50mph there is an issue. I'm not sure what it could be as this has never happened to me before.
I've pulled RV with mine-- 3.73 mind you, and when climbing a step hill starting in overdrive at 70 mph holding the pedal near the floor, it will slow to ~62-64mph where it will downshift to 3rd. If the steep grade persists, as soon as my speed drops a few hairs below 50 it has reached downshift threshold again and will probably downshift to 2nd. Maybe i've misinterpreted your problem but that doesn't seem right.

if by 55 mph it has not shifted out of overdrive, do it manually. Or better yet, if you can read the hill in advance, manually shift it down to 3rd before you even hit the hill. It will keep your momentum up and have way more power for the hill.
 

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Discussion Starter · #4 ·
I will usually try to get a run on the hill to build a head of steam but it will fall of pretty fast even with the 4:10s . At this rate the temps skyrocket so I have to back out of it . At 55mph in 3rd I have plenty of rpm before redline so I also thought it should downshift .
 

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i have a camper and a boat. on a hill mine will downshift. never had to manually shift it. the tranny is rebuilt exchange 2 years now. old tranny would go into overdrive at 30 mph new one, no matter what will not o/d until 45 mph precisely. weird. even brought it back to the tranny shop to ask about that and he says it's running the way it should.
 

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Ah, I see what you mean. Yours probably won't downshift to 2nd until you fall under 50 because of your 4.10s.
 

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Mine won't downshift until about 52-53 MPH, but I've manually downshifted at 65 with no issues. It doesn't really lower the EGT's alot, but it gives you enough added power that you can back out of the throttle and lower the EGT's that way.
 

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mine will downshift to 3rd at 68 this is with 4.10 gears but i will back out of the throttle so that it doesnt downshift until 60.
 

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Discussion Starter · #9 ·
Silvy , it wont downshift out of overdrive into 3rd. I've been leaveing it in overdrive because she'd be redlineing at 65 mph with the 4:10s. Its just that if I pull grade with any head wind Im in trouble . I was afraid to manually pull it out of OD and into 3rd , fearing rpms would go to high but after some trying it 55mph shouldnt be a problem to drop it into 3rd .

So is there something I sould be checking to find out why it wont downshift automaticly ?
 

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You shouldn't red-line in 3rd until about 75 or so if your torque converter lockup is working. I know I've run 70 with mine in 3rd before and had more left before red-line. I have 4.10's with the stock 245/75/16 rubber.
 

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Discussion Starter · #11 ·
I was somewhat guessing but if memory serves correct I would pull 3000rpm around 55-60mph and redline on my tach is 3500rpm.
 

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are you even getting converter lockup?
 

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Discussion Starter · #13 ·
This my sound stupid , but how do I know ? It doesnt seem to have any problems as a matter of fact she pulls hard and shifts really tight . When it does lock up , is it supposed to feel like its shifting into another gear and pulls hard once in overdrive ? ( does that make sense ? ) If thats the case then yes it is locking up.
 

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Your tach may be off, very common problem on the 6.5's. I believe 60 is about 2700-2800 on mine.
 
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