trucks squeeling like a pig...kinda

[4x4orbust]

....and it's coming from under the trans tunnel.

 My 82 K10 is my plow truck. (350, th350, np208, 10 bolts)    while out plowing in yesterdays storm, i had a few instances where this happened.  only in reverse, and only under moderate to heavy throttle to back out of the snow pile.  does not do it in 4 lo, only 4 hi.   almost sounded like the noise the plow pump makes after it's all the way up.  

 also at times i had a shudder in the same situation,  but not accompanied by the squeal, i can't tell if thats the tires or not (swamper tsl's 33x12.5)  

absolutely no other issues otherwise.  shifts fine, drives as it should. 

i was thinking it may be a clutch of some sort (bad tranny), or the bolts from tranny to motor may be loose.

any ideas on where to start looking?

[Da67goatman]

check tranny fluid, it could be too low for the pump to build adequate pressure.

[86k20]

check pump belt it happend to me only in 4 hi for some reason last year couldnt figure out why

[4x4orbust]

I had checked the tranny fluid tues. night, and all was good.   didn't leak any that i can see, but i will check it. 

i didn't think of the pump belt, i usually take it off for the summer, and i put i back on about a month ago.  might not be tight enough.  although it didn't sound like a belt squeal.