My transmission seems to be slipping...torque converter??

Ok here is the situation. I have a 1964 dodge dart gt. I recently had the slant 6 bored .040 over installed new pistons. Also had the head done with new valves, springs and had the valve seats hardened. Otherwise the engine is stock to my knowledge. I also changed out the 13" stock wheels for 14" wheel and new larger tires 215/70/r14. Since then I've had slipping issues. I recently had the transmission out and found the clutches and bands to be in good condition. I did replace the clutch piston seals because of leakage during the air test. Put everything back together. The shifting did improve but still slipping. Car is slow taking off and builds speed slowly. The torque converter was put it about a year ago. Everything ran great until i lost compression on cyl #4 a few months ago. Thats when i had the block bored and head done. Along with the new wheels and tires replaced the windshield. So I've just spent over 2k on this car. Would the bigger displacement and larger wheels cause the tourqe converter setup to be off?