1 - Never EVER use stop leak. Sure, it may stop you leak AND clog some other part of the cooling system (radiator, heater core or some other problem). Crappy solution (makes one problem into a bigger mess by tempting people for the "quick/cheap" fix).
2 - If you want a 3800 just for having a 3800 (no performance modding beyond drive train swap), you would probably be better off selling your existing Monte and then buying one with the 3800 (unless there is a reason you want to keep the chassis you have).

When you were pressure testing the system, was it 13-15lbs of pressure? If you put MORE then that in, that is way beyond the amount of pressure the system is designed for and you are FORCING coolant to go out somewhere as a result.

You mentioned you had the water pump replaced. It's possible the new pump is bad or it's not in tight, hence a leak. Check all your hoses (radiator, heater and the bypass hose above the water pump), make sure those are not messed up.

 

honestly..id rebleed the system and see what happens.....

 

My head gaskets never leaked. its always been just the intake. the only reason we had to replace the head gaskets was because we took the heads off to be inspected and since the front head was never the one 2 blow the gaskets i only had the back checked and im not sure how he inspected it. my uncle took it to a local place around here for me. i honestly think its warped. Am i able to put a 3.8 in this car? i was told it would bolt up to trany, but i would have to have the computer reprogrammed? is that all? cuz if that's all i have to do it only cost $100 for the dealership to do that and i will put a 3.8 in it instead of this junk 3.4. If i have to replace a bunch of wires from the harness then im not sure i wana bother, but if everything is pretty much the same then it wouldn't be a hassle. is there anything i should know about 3.8's b4 i jump to this decision? i don't trust this engine that is in my car currently and im not going to waste my money and time on it any longer. its getting ripped out....

 

the car wont LET me even put 15 lbs of pressure. it wont hold it. it wont hold more than 10 and drops to 7. the water pump isnt leaking. nothing is except at the intake. im am well aware of the damage stop leak will and can do and normally i would never ever put it in my car but honestly im fed up with this engine and will tear the whole thing out and im tearing my rad out and replacing it with the new engine also. i dont have the money for a new car, buying an engine and putting it in myself is way cheaper than buying a new one. i still owe 2k on this car also, and i wont sell a car with a bad engine. my conscious would bother me too much and i would need to get at least 3k out of it to get another one worth buying. If it is way too complicated to drop a 3.8 in this car then i will keep with the 3.4. i will try to get one with as less amount of miles on it as possible and then in 2 yrs ill probably sell the car (i say 2yrs because i have a warranty on my trany and i wont give it up till that warranty is up)