I have a 2001 Ford Mustang the water gage went from hot to real cold and car started tremble?

It has new radiator thermostat upper hose and the fans turn. What could be wrong

A water pump with a leaky shaft would not cause the issues you have. Leaks in the shaft are an indication the seals are wearing out but that doesn't mean it will have any effect on the readings of the temp. Gauge. You didn't tell us if the engine had overheated or not and that can be a vital sign of pump failure. The fluctuation of the temp gauge could easily be caused by a faulty temp sensing unit, an electrical fault or… An overheated engine. If the engine overheated it might cause what you described as "tremble". If it did overheat you'll need to check the pump as well as the radiator core for signs of clogging. On a '01 model the cooling system should have been flushed when the thermostat and hose were replaced.

But it still ran? The first thing to check is the real water temp - Is it hot or cold? The only thing you haven't replaced yet is the water pump, so check it out. One the snout of the water pump, between the main housing & the belt pulley, look for dripping water. The snout is hollow, and the bearing on the pump shaft closest to the engine has a seal one it, to keep the water out. As that seal starts to wear-out, water will get by the seal & into the hollow center of the pump. There's a 'weep' hole on the bottom of the snout, where this water will start to drip from. So if there's water dripping from the bottom of the snout of the water pump, the seal is failing & the pump will also fail soon, because the water will wash all the grease out of the shaft bearing & it will overheat & lock-up.