well of course its gonna rev slow if its not getting the electrical power it needs.
just keep looking over things as much as possible before you take it to a shop. cuz that would suck if u took it to the shop and it was some simple little thing and next thing u know ur paying an arm and a leg.
maybe a video would help someone to find out what is the problem
dont take it to a shop for that man, check the plug to the altinator both the of wires should have batt voltage when the key is on the "on" position, also the think wire that goes to the altinator should also have batt voltage check that then get back here.
do you have jumper cables? if so just take the black cable clamp and put it on the neg side of the battery then take the other black cable clamp and ground it on the engine block so it get good ground. then see if you have 13 14 volt out of the alt. and try and measure the voltage from the alt not the battery.
ps i hope i dont get ban for help you out.