99 4l60e problems

I have a few questions about the trans. in my 99 silverado 4x4. Ever since I got the truck it sounded like the pump may be making a slight wine. Well finally something went south. I parked the truck and came back out to leave and no reverse, I pushed the truck back by hand and drove the truck about 1/2 mile home and man was it screaming, kinda sounded like an old time firetruck siren. After some research I see that the sunshell may be the problem but my question is this, after parking the truck in my driveway it seems that the truck isnt stationary in park, is this also because of the sunshell? WHere is the cheapest place to buy the parts needed to fix my trans? I will prob. put a new pump in while IM in there also. Thanks in advance

Yes, a broken sunshell can cause it to roll when it park.

Here is where I get most of my tranny parts. This kit is very complete (new pump, sunshell, etc): https://www.700r4l60e.com/store/product.php?productid=37&cat=22&page=1 Note this is the heavy duty kit. They sell others but they are more street/strip oriented.

//2000CAYukon