89 Tranny question

Well i have a 89 4dr,305,700r,all power options. Qusetions is my tranny when its cold i can floor it and it will run the gears out right but as soon as it warms up kick down stops working and quick shifts (low rpm shifts
) but, i can manualy shift fine up and down ?? Also i love this car everyone trys to get it off me lol umm couple questions sorry. 1st can i change the rear end to a limited slip i belive its a chev 10 bolt and, where can i find headers for that body style for my 305 ( switching to a 350 in about month so what ever i have on 305 will work for 350 http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&rd=1&item=7918427949&category=33615 )

Thanx all alot for your help i have a website with pics of her if anyone cares lol

I do know of differentials on Jeg's that may work for the Caprice, but if you have the 305 I've found headers that fit an 88 Caprice. I believe they fit the 89 but you can check. AJ-USA has the headers listed by vehicle fit. The headers I found are Hedman Hedders with a 1-5/8" primaries and 3" collectors.