which nut? the one with the set screws?

well if you dont have it apart yet it may not have been the nut, mine never moved and had the updated shaft and all it toasted both the gears, peeled all the teeth of them.

Brake parts cleaner (or a paint shop degreaser) and then you weld it all the way around... that's what i did and it's NEVER EVER EVER EVER going to come off..

now if i have to fix anything else in my tranny, that's a whole other story... but i don't think anything else will fail on these trannys...

The easy long term solution is to stop abusing the transmission by lugging it in 5th. I know that's hard to do when the engine will easily make the pull in 5th...

its even harder not to shift into 5th when the truck only runs about 45-50 in 4th.

well i got my truck all tore apart to fix 5th gear, but i hit a snag. the tack welds i put on the first time, are still in place, the nut hasnt moved.... what did i break now???:s:
does anybody have any pics of what it looks like when 5th comes off?
n what kinda tool do i need to get that nut off?

yeah when i pulled mine apart, the nut was still tight. i've got the nut off now but the gear wont come off. i think im gonna drop the trans n pull the shift tower off n see what i can see.
i lost 5th on the way to work a week ago, i had just shifted into 5th, got back into the throttle and POP, no 5th gear, just like neutral but i can hear something grinding or rattling. all the other gears work fine. what else could have happened?

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if i put the truck in 5th, i can grab the output shaft and turn it. the big gear next to it turns also. i can hear a crunching sounds coming from inside the gearbox.

You have 4.10's in that truck? If so, then you may not be abusing the transmission after all. I thought you were lugging it based on something you said in an earlier post. The definition of lugging it as far as I've always heard for these transmissions is applying heavy throttle at or below about 1500 rpm. If you have 3.54's and can't get more than 45 or 50 mph out of 4th, what rpm is that?

if you have all other gears I believe your problem would be on the counter shaft 5th gear assuming the gear on the mainshaft is still on there.