pop a pressure tester on the rail, see what your getting, you need 43 or more to run well.

i got a 5/8's rad a 195 t stat, fans tuned to 180, and i dont get much over 205. same as it ran with the one inch rad that cracked. same temps with the l67 that is as. and the same now with the bottom swap set up now.

your rad might be clogged up, or the water pump is rotting away. or your fans dont turn on as they should?