Charging problem

I recently converted to a reman'd 95GT alternator, and I'm still only getting like around 11.8 and dropping when i drive. I don't have a belt tensioner, do you think it could be slipping that bad? I put the old pulley from my 2G alt. on there too. I have a 175A fuse. could it be a bad ground somewhere maybe? i made sure all my engine>battery and engine>chassis grounds are right?????please help

It drops, just very very slowly, so i assumed that the alternator is at least trying to charge it

Actually that ground has one 8ga cable that runs to the top of the firewall right behind the upper manifold. I couldn't get the damn nut off to take it off, so i slapped a 4ga down on top of it, and put a nut over it, then ran it to the area shown in the battery.
I ran new 4ga wire from the ground on the front of the block to the battery ground terminal.
I have the two original 10ga wires running off the back of the alternator to the solenoid (bout 8-9ft long, runs around the back of the engine bay), and one 4ga wire running from the alternator directly to the positive battery terminal, only about 3ft long, and it runs alongside the distributor.
Also, yesterday i sprayed quite a bit of belt dressing on my belt and it seems to be charging semi-ok. It's not really going below 12V, and is usually around 12.3-12.4 (I have a aftermarket voltmeter inside the cockpit). I just want more voltage so i can drive at night. What voltage should i generally be around? Plus I don't have a belt tensioner....maybe the problem?

Well i have to wait two more paychecks. I owe my mom some cash and the belt tensioner's like 90 bucks at advance, and I have no idea where there are any pick'n pulls around here.