Dodge dakota infinity replacment speakers?

Do yourself a huge favor, rip all the factory infinity junk out, get a nice head unit and and round out the other speakers with matching ones and be light years ahead on sound. If you are feeling frisky add powered sub and a head unit with Hight pass and low pass frequency filters. Block the lows to your doors and highs to your sub.

No need to measure amps or volts at the speaker. measure the resistance, ohms, by measuring at the + and - terminals of the speaker.

If the rear speakers were 2ohm and you replaced with 4 ohms you have lost 3dB of sound.