Trans question on RT14615 o/d ???

well i had a bit of a question my truck has been doing this since i bought it and it has me a little wondering why it does so. Well the truck when its cold loaded or empty is fine i would say about 30-50 miles into a trip if truck is loaded at about 80K less or more it still does it after getting warmed up on the expressway at 65mph the faster you go the more audible it is and you can feel it. when im in high range of course and in last gear "15" i will be humming along on straight piece of road with no issues then when a hill or overpass approaches i will climb it and when im coming down i will let out of throttle just a bit to keep speed even and i will get a strange growling,grinding or rattling noise coming from what sounds to be the transmission somewhat DULL noise not high pitched this is with windows up. it only does it when coming down off a grade in the last gear or lets say im on a staright piece of road i take it up to 80mph and when i let off just a little bit not my foot off throttle but just a lil then it will do it as well, but in both instances if i just pull my foot off real quick with no throttle blip at all it will not make one noise or growl... Im prtetty sure its coming from trans as i put my hand on shifter handle when its doing it and i can feel it for sure thru my hand.

now my diagnosis is this:
1. When its cold within its first 30-50 miles it wont do it loaded or empty.
2. When it warms up afters these miles it will do grinding noise (loaded or empty)only when decelarating but with foot still on throttle just a little bit.
3. Will not make noise at all if i pull my foot out of throttle completly and just let it ride down with no throttle blip at all.
4. Trans temp guage the whole ride doesnt go past 175 degrees and trans has good fluid (not burnt) and an external trans cooler.
5. Will only make noise when decelerating while foot is still a little on the throttle pedal if i run with throttle given the whole time like normal you will not hear or feel noise if accelerating normal.


is this a bad last gear or syncro. trans doesnt grind,goes into gear great,never misses a gear shift,doesnt overheat. Whats the deal?????

i hope this isnt bad news for me and is something that can be done from rear of trans and hopefully trans doesnt have to be dropped completly.

any help would be great thanks.

 

well no play on the rear of the trans on the yoke, and i had a new bearing and input shaft installed as the old one was toast when i did the easy pedal clutch on my truck at begining of the year.
doesnt make the noise when im costing loaded! and another thing is that when its bobtail it doesnt do it at all warm or cold. it doesnt do it when im on the thottle, doesnt do it when im coasting,and it doesnt do it when i let off throttle completly.

ITs like at a little bit less then coasting slight throttle applied.

could it be an actual gear inb trans for that speed is chewed up....

 

it has to be the original unit from the truck as is all other drivetrain components 1.6 mil on odo

 

i will check it seems to be in line with all other driveline components.

 

you wouldnt believe that since lowering the front of the truck its actually gotten rid of this grinding noise i dont know its left me stumped lol but happy.

 

i could understand how it changed the angle but the leveling valve is still level. truck has a slight rake not much. and level valve is on rear drive not front one.