Just found out after hooking up my sr5 dash that the combo voltmeter, ohm meter / tach that i have was reading rpm incorrectly. its one that has its own battery and only hooks up to the neg side of the battery and another wire to the diag terminal on the coil. I bought it for like $35 from Harbor Freight. In order to have it read correctly i had to switch it from 4cyl to 8 cyl.

Keep this in mind if you have at least a carbed motor and a combo meter like i do.