Tacoma front speakers inquiry

I have recently purchased a 2012 Tacoma Sport 4x4 Double cab. The original package was the Entune/JBL system. It appears that the previous owner upgraded the component speakers and amp for the component speakers. I have noticed that the front door speakers only play the low frequency. I have messed with the low pass filter and the high pass filter on the aftermarket amp to no avail. I have pulled the front door panels off to see if there is a crossover or something that may be impeding the signal and there is not. There is also no x over attached to the amp that I can see. I have not pulled off the plastic cover behind the back seats to see what is behind there. I doubt that JBL and Toyota made these front speakers woofers from the factory. I had an 05 Taco Access Cab before and it was full range sound from the front 6x9s. Any suggestions?