If I get some performance parts for my car can i get a new speedometer with a higher top speed?
You can get a faster speedometer (yours came with 120mph), but for a 1994 V6 you will need to recalibrate the speedo which can be difficult. A calibrator module will run around $100 starting out. You can also simply change the speeod gear in the transmission, though it is not as accurate. All in all, the only way to change the top speed in one is to change the rear end gearing to a shorter gear (which will cost you take off speed) or to change the gearing in the transmission (also costing you take off, and can be rather pricy). All in all though, simply plugging in a GT (150mph) speedo or a Cobra (160 mph) will not work.