E4OD
Fleet Owner
Joined: Oct 2005
Posts: 20,783
Likes: 1,751
From: Kentucky
With the very large tire change the computer is basing up and down shifting on outdated and very out of range information. I would fix what I know is wrong before going down any other bunny holes. If the truck was already saddled with very high gearing (numerically low, i.e. 2.73/3.08/etc.) those 35" tires are making a bad situation worse.
Fleet Owner
Joined: Oct 2005
Posts: 20,783
Likes: 1,751
From: Kentucky
A "posi locker" will only facilitate getting power to both rear wheels. You have to change the ring and pinion on both ends to something more compatible with 35" tires. On a 4.9L engine you need a lot of multiplication to overcome those large wheels/tires as well as modest torque that engine delivers. Getting the PSOM recalibrated for those tall tires will help as a starting point.
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New User
Joined: Nov 2021
Posts: 21
Likes: 0
So i reset the PSOM and it feels better but it still has the problem with the transmission which i mentioned before and looses throttle response around 60 after the down shift and slots the rpms in between 1000 and 1500 but it has no saved codes or tripped codes im at a stump with it now
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Joe Kucinski
Fleet Owner
Joined: Oct 2005
Posts: 20,783
Likes: 1,751
From: Kentucky
Did you have any issues with acceleration before you installed those 35" tires?
Check the sticker on the driver side b-pillar for the Axle code to see what the gears the truck left the factory with. How old are the spark plugs, wires, cap and rotor? Same for fuel and air filter?
Check the sticker on the driver side b-pillar for the Axle code to see what the gears the truck left the factory with. How old are the spark plugs, wires, cap and rotor? Same for fuel and air filter?
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New User
Joined: Nov 2021
Posts: 21
Likes: 0
and while im trying to figured this out can you also help me out my buddy was messing with my hood latch and locked it while i didnt know so when i got done i closed the hood and now it wont open and is not all the way down any idea how i can fix that too
Fleet Owner
Joined: Oct 2005
Posts: 20,783
Likes: 1,751
From: Kentucky
Right there....3.08 gears. Even on stock tires that gear ratio was a dog especially with a 4.9L engine. Those 35" tires and the added drag/weight have further strangled the engine. IMHO there is nothing wrong with the transmission, you are simply out of power to overcome the monster shoes you installed. Then add the lift to the barn door aerodynamics of these trucks. You need a lot more gear to get yourself back to the starting gate let alone any performance gain.
Fleet Owner
Joined: Oct 2005
Posts: 20,783
Likes: 1,751
From: Kentucky
I have had to reach up between the grille and radiator to pull on the release cable once or twice when that happened to me. Tough to do with short arms...
Fleet Owner
Joined: Oct 2005
Posts: 20,783
Likes: 1,751
From: Kentucky
A 4.56 gear with 35" tires will run at ~2000 RPM at 65 MPH. That is the torque peak RPM for your 4.9L engine. You need to overcome a lot of variables (lift/tall tires/extra unsprung weight/etc.) so going big on gears is not out of bounds here. Others will have their opinions but those 3.08s have to go or go back to a shorter tire.
If you do a lot of in town driving 4.88s are viable. If you drive mostly highway and/or faster speeds 4.10 may work, but my vote is for 4.56. Make sure you keep that 4.9L engine in good tune and consider replacing the factory exhaust with something a little freer flowing with a modern 3-way converter. A V8 swap would bring easy torque gain for the money spent, but nothing is going to be easy here.
Even with gearing changes you are not going to regain much in MPGs. You have ~260 lb./ft. of torque that comes in at 2000 RPMs. It drops pretty quickly from there.
If you do a lot of in town driving 4.88s are viable. If you drive mostly highway and/or faster speeds 4.10 may work, but my vote is for 4.56. Make sure you keep that 4.9L engine in good tune and consider replacing the factory exhaust with something a little freer flowing with a modern 3-way converter. A V8 swap would bring easy torque gain for the money spent, but nothing is going to be easy here.
Even with gearing changes you are not going to regain much in MPGs. You have ~260 lb./ft. of torque that comes in at 2000 RPMs. It drops pretty quickly from there.