1996 GMC Jimmy cooling system problems

The dealership had done all the service work since I owned the vehicle,at 47,000 miles the anti-freeze had the consistency of syrup and was clogging up.after much complaining the dealer pulled the radiator had it flushed and refilled.approx. 30,000 miles later the same thing.they flushed and filled again.it's doing the same thing again in less then a year.they refuse to correct the problem.they informed me I had to pay for it myself.it was never corrected to begin with.

Engine and engine cooling:cooling system. Engine coolant has broken down at 60,000 miles 10/1/2001, 70,000 miles 6/1/2002, 79,000 1/30/2003 and has became sludge. Owner's manual states 100,000 mile maintenance. Dealer (GMC)wants to replace thermostat, radiator, heater core at my expense. System has been super flushed, cleaned and new dex-cool coolant per dealer recommendations. Dealer even states coolant is bad. GMC states iit is my fault.