I'm unable to locate the post or poster who wrote about how he could alter his shift points all the way into 4th gear by using the T/H switch on a 2005. Someone else later said this was also true with 2004.5 through 2006. That was a ray of hope but, in my case, it turned out not be so.

The 2004.5 shift pattern is not like that described for the 2005, at least not in my truck, which was built 6/2/04 and delivered 8/4/04. Shift events occur as follows: (20-25% throttle)

Tow/Haul off (not-illuminated): 1st = 0-15mph, 2nd = 16-27mph, 3rd = 28-43mph, 4th = 44-49mph, TC lockup at 49mph.

Tow/Haul on (illuminated): 1st = 0-15mph, 2nd = 16-27mph, 3rd = 28-46mph. At 46mph there is an event where the rpm drops 200rev. I think this might be a TC lockup in 3rd. But it is unlike the TC lockup in 4th because the tachometer will drop about 400rpm when you get off the throttle. The drop is from 1800 to 1400rpm, and the truck also slows under compression braking. If it is a TC lockup, then 3rd gear in the transmission must have a lot of fluid coupling going on. 4th Gear never happens with T/H engaged.

When cruising in fourth with the TC locked up (50mph and almost neutral throttle) and switching into T/H, there are three events. First the TC unlocks and the RPM jumps upward (to about 1600rpm), an instant later the transmission shifts into 3rd and the RPM climbs up to 1800rpm. Then the TC locks again and the RPM shifts upward to 2000rpm. All this happens in about two seconds.

When cruising in third at 40mph and switching into T/H, the rpm jumps from 1500 to 1700. Not sure what happened, as this is slower than the typical 3rd gear TC lockup. Maybe that was a 4th unlocked to 3rd unlocked event. Don’t know.

Being in T/H while climbing keeps the transmission from doing the annoying 3rd to 2nd downshift in the 30-40mph range. Glad to discover a solution for that problem.

Now one has to wonder…if a 2005 box (ECM?) were be to installed on a 2004.5 truck, could we get the 48RE to shift into 4th with the T/H engaged AND get the TC to lockup at any point while in 4th and T/H engaged. (Essentially how the 2005 was described earlier.) This would be a nice solution.

 

That would be the simple way, but, it ain't gonna happen. The 05 autos have more electronic controls and TQ management. The hardware is not there for the 05 ECU to work correctly. Don't feel too bad though, not sure whether all the new stuff is that great. A lot harder to find a fix for less than adequate shift patterns.