i was told today that i could only use dealer fluid in my 98 spyder....i am just trying to change the filter and pan gasket. do i have to buy from them or can i use an off the shelf brand at auto zone, advanced, etc.?

A/T tranny = very picky.
Diamond ATF is good stuff. It's only $4.48/qt. =P

so how many quarts will i need to refill it after i put the new filter in? 4? 5?

5-8
http://www.plymouthlaser.com/atfaqs.htm

if you did the regular drain/change the filter and gasket then start out with 3 quarts and keep checking till its full. The gs spyder capacity is only 6.1 quarts so make sure you dont overfill tranny will shift funny and spew oil everywhere. You dont have to use dealer brand atf, reason why the probably tell you that is because the dealer atf has a higher coificent than other off the shelf atf. You can use other brands of atf that meet the requirements but also use a bottle of lubeguard (the black bottle) My suggestion is that if you do some hard driving then use a synthetic along with a bottle of lubeguard