I just went through this with both of my WJ's.
I replaced one speaker on each of the WJ's with the cheep 2.5" from the on line site. Worked great.
When I was forced to replace the second front speaker on each they only workded for a few hours. I went to the $tealership and purchased two (one for each WJ) and installed in each jeep.
Works great again. It turns out that the cheep speakers are just too high resistance. the factory 2.5 ohm's brought the total resistance back down in line.
So, $5 for the cheep on line speaker and 60 for the factory speaker. I spent 65 dollars on each WJ for new front tweeters. Problem solved.