Struggles to accelerate

Struggles especially when depress gas pedal. Sounds like it will stall but has not. What should I check first? Let me elaborate on skill level. I know more than the average person about my car. The basics (oil change, tires, etc) plus a few repairs/replacement parts in detail of my car only, ie: alternator, starter, spark plugs/gaskets. Working on replacing thermostat, just bought it yesterday.
She has been running hot just after freeway driving for about fifteen minutes. I have used gasket leak liquid twice, worked for a several months then got hot, water spraying out of reservoir. At least one collapsed hose. Replaced the two in the front, upper and lower. Then flushed cooling system. Not sure if I 'burped' her correctly, since she keeps running hot. Upon recommendation, I was getting ready to replace thermostat. But on my way to work this morning, she just would not pick up speed unless she feels like it. Accelerates at times even though I am not stepping on the gas and hesitates when I do. I have a book and can look some stuff up. But it is not very detailed. And the pictures are horrible! I am hoping you can guide me though this. Considering picking up a code reader, OBDII?