Hard 2 start when cold when running it bucks and****** smooths out when u give it gas

So you did change the coolant temp sensor with a black wire and yellow going to its connector?Also did you inspect the terminals inside the connector to make sure there not blue or green instead of silver?Also if you got the wrong sensor like the one for the gauge on the 1995 saturn S model that will cause issues also.

Since the head gasket replacement it hasnt run right?How does it run?Any codes?

Are you spark plug wires routed correctly?How are your spark plug wires and spark plugs?You dont have platnuim spark plugs in it do you?

As far as the heat goes is both heater hoses getting hot going into the heater core thru the fire wall?

Have you done a compression test yet?If not I would do that next.

Normal compression is 185-205psi min compression for a good combustion is 180psi. So theres your problem your compression is too low. No wonder it runs so bad. Are you sure the cam timing is right?

I posted the timing marks for you. You have to remove the valve cover and then rotate the crank pulley around untill the timing marks on the timiming cover and harmonic balancer are aligned. Then check the dots on the cam gears they should be straight up and the 3/16" inch dowl holes in the cams should be aligned also. Get some 3/16" drill bits to make sure there aligned. Let me know what you find.