Truck starts but won't engage in any gears

See the link for a video (part 1 of 2) with excellent guidance on your issue. Valve body removal starts at about 9 minutes. Make sure you have disconnected the large electrical connector that is connected directly to the valve body.
Part 1 2 45RFE 545RFE 65RFE and 68RFE transmission shifter linkage will...

check shifter cable. if you want to start it first, look for the lever that connects to the transmission and shifter cable and manually move it until it reads part or neutral and start it.

Transmission gears not engage could be low fluid a torgue converter problem or transmission wearing out

Transmission won't engage Drive or Reverse - EricTheCarGuy

www.ericthecarguy.com/.../53999-transmission-won-t-engage-drive-or-r...

This transmission shifted smooth and strong through all gears until today when it stopped all of ... Any idea on where we should start tackling this issue? .... Also, make sure that the pressure tester is not leaking or you will run the tranny dry(use ...

Gear shifter goes from park to drive with no effect. Won't ...

I would check the linkage in the shifter. Also on the transmission, check all the connections.

Can be issue with transmission or its related components.Many car models face such problems.

For complete step by step troubleshooting,few help links are provided below.Click the link below and go through its procedure to resolve the problem:----
Engine misses and truck jumps? Hard to down shift? Issue with high gear only? http://technoanswers.blogspot.in/2012/02/engine-miss-and-truck-jumps-hard-to.html

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Car sitting for year, now will not crank and go in gear? http://repairhelpcenter.blogspot.com/2012/01/car-sitting-for-yearnow-will-not-crank.html

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2004 Peugoet: Clutch not going in gears?
http://whoisbyme.blogspot.in/2012/05/peugeot-307-clutch-will-no-go-in-gears.html

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Engine stumbles and shuts off in forward gear on Toyota Land Cruiser? http://schematicsdiagram.blogspot.com/2012/01/engine-stumbles-and-shuts-off-in.html

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Transmission problem? http://schematicsdiagram.blogspot.com/2012/01/transmission-problem.html

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Car engine Overheats and transmission starts slipping?

http://schematicsdiagram.blogspot.com/2011/12/car-engine-overheats-and-transmission.html

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Manual Transmission Clutch System Failures?

http://repairhelpcenter.blogspot.com/2011/11/manual-transmission-clutch-system.html

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Automatic transmission will not go into high gear? http://howtobyme.blogspot.com/2011/11/automatic-transmission-will-not-go-into.html

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Manual transmission very hard to shift from one gear to another? http://repairhelpcenter.blogspot.com/2012/01/manual-transmission-very-hard-to-shift.html

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Dodge manual transmission will not go in reverse gear? http://technoanswers.blogspot.in/2012/02/dodge-manual-transmission-will-not-go.html

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2006 Chrysler 300c: Shifter Stuck in Park? http://technoanswers.blogspot.in/2012/06/2006-chrysler-300c-shifter-stuck-in.html
---------- 1998 Ford Expedition: Will not Shift Out of Park? http://schematicsdiagram.blogspot.in/2012/06/1998-ford-expedition-will-not-shift-out.html
---------- Car will not move when in gear?

http://repairhelpcenter.blogspot.in/2012/02/car-will-not-move-when-in-gear.html

----------- Mercedes-Benz transmission sticks in first gear? http://technoanswers.blogspot.com/2012/01/mercedes-benz-transmission-sticks-in.html
---------- Mercedes Benz not engaging in first gear? http://technoanswers.blogspot.com/2012/01/mercedes-benz-not-engaging-in-first.html
--------- Chrysler PT Cruiser only goes in First gear?

http://howtobyme.blogspot.com/2011/11/chrysler-pt-cruiser-only-goes-in-first.html

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Car is stuck in park and the shift will not move?
http://howtobyme.blogspot.com/2011/08/car-is-stuck-in-park-and-shift-will-not.html

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These details will help.Keep updated for more help.
Thanks.

Under hood next to master brake cylinder.it dos sound like a clutch / or clutch fluid problem / there will be a black rubber in it that you have to remove to add fluid / it is round / hope this helped Good Day.

Most likely solution is the gear selector fork in the transmission has broken and is no longer engaging the gears.

Repair requires transmission removal and partial overhaul.

Unfortunately any problem it could be will have the same fix. You will end up needing the trans replaced or rebuilt.