Replacing expensive components in the hope of stumbling upon a fix is likely to send you broke. You really need to plug an OBDII code reader into the vehicle's OBDII diagnostics port to see where the problem lies.

You should be able to buy an OBDII scanner from eBay for under $10 (including software) and use your laptop or android phone to get a readout of the fault codes, as well as other relevant engine data. Until then, I wouldn't be replacing any more parts purely on spec.