The gauges are basically ohm meters and the sending units are variable resistors. You can test the resistance of the senders. If they are in range, then there is no reason to replace them and the problem is in the gauge cluster. To test the gauges, you can tap the leads to the senders together and see if the gauges jump. (I've never done this, so someone correct me if this would damage the gauges, but I don't think it would)

88 Reg Cab 22RE 5spd, Mods: 94 bed, Sunroof, Bucket Seats, PW, PL, AC, Keyless entry, remote start. (Practically a Lexus)