New wiring mains problem

I finally finished and installed my new set of mains cables. 2awg welding cable, crimped, heatshrunk, ends wrapped in electrical tape. However, when I installed the cables (only positive cables and the block-->firewall neg. cable-the others have been installed for some time), the jeep actually took several more revolutions to start and ran rough, as well as idling lower than before. I've tried wire brushing all the paint off the contact points and using star washers, but it only helped a little. I also tried using dielectric grease on the negative grounds but it seemed to make it worse.
Help!

While I doubt that this is your basic problem, dielectric grease is an insulator -- you need something such as Ox-gard to increase conductivity.