8ohm to 4ohm split to center channel mono? HUH?

So I began upgrading my 2017 Ram 2500's audio system. This isn't my first time around the block when it comes to car audio as I think my first system I put in was say...2000ish. I've never had a problem till now. The factory audio system comes with 6 speakers with a possible 8 if you get the premium alpine system. (The premium comes with a sub and a extra center channel in the dash)  That means the two dash speakers have a center channel in my truck that was empty. I decided that and extra 3.5" speaker needed to go in there while I was swapping the factory 2 front 3.5s" I ran signal from left channel positive and right channel negative to the center speaker making it mono.

Here's the rub: The factory dash speakers I pulled were 3.5" 8ohm 15w. I installed 4ohm 90w Kicker CS series 3.5s. I also found out online that the two front door speakers and the two dash speakers are run in parallel. Hooked up with the balance centered the center channel speaker sounds awful...barely any tone with crackles and weak "barely there" sound. If I isolate the balance to either the left or right signal it actually sounds fine. 

So I know that the front door speakers are 4ohm and the deck speakers were 8ohm. That mean the factory was running a 6ohm load before I replaced the deck speakers with 4ohm 3.5"s

What should I do the get this right?