a couple times lately, on cold mornings, i've started the truck, warmed it up, jump in to back out the driveway, put it in reverse and nothing, its like i'm still in neutral, engine will rev, but no go...no sounds, no clunks, no grinding, just no reverse.
i put it in drive, move forward an inch, then try reverse again, and it goes in no problem. anyone experienced this before? fluid level is good.

I was told to put it in forward frist, and you mite try put in neutral not park to warm up
the oil

Somewhere inside the 4L80-E is a piston which is made out of plastic and is notorious for cracking and failing. It is relaced by $60 upgrade kits I've seen on E-bay. Check it out because I've also read that when this piston fails it can shift your truck into reverse at any given time, like going down the highway at 70. The kit also claims to fix all the known quarks in the 4L80-E.

mdt that is a filter and it is right at the end of the manuel valve in the valve body

i guess its time to have someone look at it.
can't leave it in neutral in my driveway as i'm on a slope,,,it'll roll right into the house if the e-brake slips. i've never had this transmission serviced other than scheduled fluid change. is this an easy repair, or a major rebuild effort?

I can only re-iterate fragment's of what I've read, but the kit has the parts to do a stage 1 or 2 upgrade, probably depends how deep you want to get into the tranny, for each level. There's also a stage 3 which makes the tranny manual, which is too far for me.

i've built tons of these things and you are probably looking at a rebuild the weakest part of this trans is reverse . the reverse band breaks, the reverse servo cracks , the bushing in the centre support wears out and chews up the teflon sealing rings and the back side of the reverse/direct drum the reverse boost valve in the pump wears out and when it sticks it supplies un regulated line pressure to the reverse circut up to 600 lbs will crack the reverse/direct piston or blow the back right out of the reverse direct drum so you get an idea what goes wrong with these trannys ..