2000 chevy monte carlo motor miss

recently had transmission rebuilt in car, when I picked it up motor now has a miss and the voltage gauge flucuates. Trans shop told us we need new plugs and wires but they were replaced a year ago when tuned up. We have replaced the battery, and starter (both tested bad) alternator tested good reading about 13.3-13.5 we are running out of options other then the plugs and wires…please help

Any codes please post

No codes, no check engine light. And to add to it now, the new battery is dead. Took the alternator out, had it tested, and now it comes up bad. We are at our wits end with this car so any help is greatly appreciated…Thanks

Well the plot thickens…the alternator rebuild shop says the alternator is good…and he wont rebuild it. He said it could be that something is draining the battery, but that since the battery was disconnected for so long that the cars “brain” needs to re-learn the car! What? you say, well thats what I said anyway. The Repair Manual says the same thing and I am like you have to be kidding me right? He said the car is relearing and that the miss will work itself out. SOOOOO dear hubby puts the alternator back in, cahrges the battery, car wont start…jump starts the car, drives it for an hour straight, comes home, turns it off…you guessed it CAR WONT START…UGH!!! If it isnt the alternator, WHAT CAN IT BE???/