when climbing hills the engine hesitate and it seems it's loosing power the spark plugs,fuel filter and iac were changed?

Try checking out the carb and compression.

I am having the same problem, but I know the engine wants to over heat when going up hills as well. I am changing the thermostat and have a code for running lean. Can these two be related or do I most likely have two different problems at the same time?

fuel/air ratios can cause temprature variations,your best bet is having a tune up.