currrently right now im playing through a peavey usa made practice amp from the 80's or 70's (i don5t know but its really old) and a squier vm jazz bass and im wondering what a good amp would be for a good slap bass sound.

SLAP BASS (> sweep pckng
I have a Hartke HA2500, it's amazing. Just Boost the low-lows, set the low,mid, and mid-highs up gradually and cut the high-highs out completely, there you go.