yesterday my truck wouldn't move at all in reverse so I put the truck back in drive then back again to reverse then it backed up why would it do this?its been doing maybe once a week for the past few months.

 

Sounds like a valve body issue that it won't build line pressure in reverse. Try this for fun. After letting it sit over night, or however long it takes for reverse to fail, start the truck in neutral. Let it idle for a few seconds and try reverse again. If it works after sitting in idle you have one or two problems. The stock valve body in the trans will not build line pressure in Park. For some reason, it sounds like it's not building line pressure in reverse either. Normally, it will build pressure in Reverse though first gear including neutral. If it only happens in Reverse, I think you'd have to take it to a transmission shop to read the computer.

With all that said, have you checked the fluid level with the engine hot and running?

 

Here is a TSB that may help.

This bulletin is supplied as technical information only and is not an authorization for repair.
SUBJECT: 45RFE / 545RFE Trans - Delayed Engagement Due To Cooler Return Filter Replacement
OVERVIEW: This bulletin involves a transmission delayed shift condition that may occur following the replacement of the internal cooler return filter.
MODELS:
2000 - 2004 (AN) Dakota
2000 - 2003 (DN) Durango
2003 - 2006 (DR) Ram Truck
2004 - 2006 (HB) Durango
2002 - 2006 (KJ) Liberty
1999 - 2004 (WJ / WG) Grand Cherokee
2005 - 2006 (WK / WH) Grand Cherokee
2006 (XK) Commander
NOTE: This bulletin applies to vehicles equipped with a 45RFE or a 545RFE automatic transmission (sales code DG4 or DGQ respectively).
DISCUSSION: The customer may experience an initial delayed shift engagement following an extended off (not running) period of time, generally after being parked overnight. The initial shift engagement may feel like a delay or slip when a transmission gear (reverse or drive) is first selected after engine start.
The customer may not have experienced the delayed shift engagement until after the transmission has been serviced, where the cooler return filter was replaced during the service and/or repair.
The condition is not detrimental to the transmission but may cause concern with the customer.
The above condition may be caused by a suspect cooler return filter a part number of 04799662AB. This “AB” suffix / level filter may allow transmission fluid to drain back out of the torque converter. The drain back condition may occur over a period time when the
NUMBER: 21-015-05
GROUP: Transmission
DATE: September 01, 2005
engine (and transmission) are not running. With less fluid in the torque converter a delay in gear engagement may occur at engine start up while the torque converter fills to its proper fluid level.
All 04799662AB cooler return filters with the “AB” suffix are suspect. The above condition may be corrected by replacing a suspect “AB” filter with a new cooler return filter whose part number is 04799662 (with no suffix or with a suffix that is other than the “AB” level).
NOTE: The cooler return filter, p/n 04799662, will not be available until September 09, 2005. The filter part number is stenciled on the side of the filter case.
NOTE: A replacement 04799662 cooler return filter may come packaged with a separate threaded adapter stud. The threaded adapter stud is used to attach the cooler return filter to the transmission. Inspect the stud and note end without threads. Install the stud end without the threads into the cooler return filter and tighten the stud-to-filter connection to 18.6 Nm (165 in. lbs.). Once the threaded adapter stud has been installed to the cooler return filter, install the assembled cooler return filter to the transmission and tighten the filter to 14.1 Nm (125 in. lbs.)
Fig. 1 Transmission Filters - 4X4 Shown
1 - PRIMARY OIL FILTER
2 - COOLER RETURN FILTER
3 - COOLER RETURN FILTER BYPASS VALVE
4 - VALVE BODY
POLICY: Information Only

 

He nailed it. That technical bulletin was something I finally came across in 2009. Problem was I'd been dealing with it since I bought the truck in 2004. I'd get in, start it, pop it into reverse, "nothing". I'd give the "WTF" look and sometimes hit the pedal thinking maybe I was on an incline or something... Only thing that it would do would rev,, engage into gear finally, and then trip the check engine light. UGH... I wasted about 300 bucks bringing it to the dealer a few times so they could try to figure it out. It would trip them a tranny code but all they knew to do was drop the pan and inspect. Anyway.. as it does say it is relatively harmless and really a quirk.. I never did get the new part. I do plan to but once I figured out what it was I merely slowed down. Meaning I start it, let it idle for a few seconds, put it into gear, wait for the feeling that it engaged, and then go.. Its only when I hurry into the truck, start it and try to drive away immediately that I get the pause and delay into gear.