Temp guage shows hot, pegs out hot after drive 5 miles, when guage showing hot, power sluggish in forward gears

9-18-15 replace alternator, 9-12-15 replace battery, 8-25-15, check fan clutch-OK, 8-7-15, replace thermostat, flush cooling system, says may need radiator-but no radiator leak, 6-25-15, tune with 8spark plugs & 1 wire set, 6-17-15 (transmission slipping or does not engage in forward gears) overhaul transmission, now have overheat temp gauge hot, cannot determine why gauge shows hot, afraid to drive may make worse, could be a faulty gauge, bad sensor, cracked block, head gasket leak