What is wrong with my car?

Any help is appreciated. My 06 Ford Taurus SE is giving me trouble. I have had it almost 3 yrs with a few problems like had to replace a starter and battery. I am having problems with it now. It will not go over 35 mph. And up hills it barely goes. Then i have a busted water pipe behind the thermostat housing that people are saying it needs to be welded or braised. I need to know why is it that giving it gas but not going that limit, what could it be..the mechanic i had ruled out the transmission and catalytic converter. I need help!

Sound like the metal heater pipe that goes to the radiator to the heater core in the firewall is cracked. You have to repair or replace soon. In the meantime, check daily that the coolant level in the coolant reservoir is always at the min. line. Do you get enough heat in the car? Did the mechanic scan the car for trouble codes? I would suspect a sensor or vacuum hose issue and that the Service Engine Light would be on. Find another garage to help you.

Thanks for the answers..ill have the sensors checked..my fuel system was done by Jiffy Lube and they told me everything was ok..then i had a mechanic told me it was the tranny, then another mechanic say it was not my tranny..but i have heard it may be my sensors..so i will get that checked asap.