down shift problems

[Cyamaha2007]

I have a 95 trans am that doesnt seem to down shift unless i have performance button on. If i dont it fells like a slug and it just pulls in that gear and then some times it will down shift
thanks for the help
Charlie

[LS13RDGEN]

I say start with the normal stuff.
Check fluid level and color. How many miles does the tranny have on it? When is the last time you changed out fluid/filter?