engine overheating problems

[zeldaVW]

hi i have a 2003 1.9 tdi 130. engine overheats anytime i put any stress on the engine, like going uphill. will go right up to red once i stop it shoots right back down to 90. also would effect the heating in the car, goes freezing an speed of air goes up and down itself. checked all obvious problems, new thermostat new radiator, checked head gasket, water pump was done recently with timing belt. its also drinking a lot of water but no leaks all the pipes are fine and the fans. has anyone else had this problem? could it be water backing up in the heater matrix maybe?? thanks