poor mpg and lack of power, maybe drivetrain problems
 

Okay so i have a 93 cherokee sport with 96k miles. She used to tear up the road had good mpg and was beating power stokes off the line at the red light but now sence i changed my tires back to my 31 inch at's from my really wore down 32's. thigns havent felt right at all. im due for an oil change like now and i got a little oil leak and im pretty sure its the valve cover gasket so im replaceing that. Im pretty sure spark plugs i need for sure because i dont think they have every been changed. My break are toast from hauling a 4 thousand pound lawnmower trailer. I need new breaks and drum breaks along with better shocks then ranchos that blow the d. But the motor is like pooping along idk what is wrong if the drive train is messed up or what it seems like the rpms are reving higher then normal. like going 35 mph it be at 1500 rpms now its at 2000... something is not right. that an the oil pressure gauge has like died on me idk what happen to that. i want it back to normal. idk if it could be injectors or the compression or what, that and the check engine light has never been on. i dont know what to do.