Sluggish acceleration after new tires

I just got 4 brand new tires for my 2002 Pontiac Grand Am. I know there is a breaking in period, but it feels almost like the car is pulling a heavy load when I am driving at times. I also just had the intake manifold, O2 sensors, catalytic converter and spark plug wires replaced (courtesy of a coolant leak). There was a brief period between getting the new tires and having the engine work done. I could tell a difference (for the better) after getting all the engine work done, and thought new tires would only make it better. My check engine light is not on, and I just recently passed emissions. Gas mileage has decreased slightly, probably due to the new tires. I have had the tires for only a week, and also had an alignment job done when I had the work done. The tires I put on my car are all season/performance Firehawk GTs. I have also noticed that I can hear a click when I change from park to reverse, and reverse to drive. I had my transmission inspected and the mechanics said it was just the engagement and that it is normal, especially on a car that has 150K+ miles on it. The clicking noise has probably always been there, but I had my windows down when parking my garage with the radio off for the first time in ever, so I noticed it then. My transmission is not slipping, though sometimes to get up a hill, I will have to give it more gas, thus causing the rpms to go up, but the car also accelerates upon doing this. Any ideas? Is it possible that this is the way that my car should have been driving all this time, but instead I got used to driving on bald tires and exhaust problems?