qldit

Good Morning aaronoxf, it is common with newer radios to have poor reception performance due to extra amplification in the RF stage being no longer used. (cheaper design)
This kind of problem was also further evident with older antenna getting water in their "air cored" coaxial cable that is used, but you have replaced your aerial so that more or less precludes that as a possible problem.

Generally when a radio is freshly installed there is a procedure for trimming the aerial to the radio, this is normally done with the aerial extended and selecting a very weak station usually at the high end of the band on AM then adjusting the trimmer in the radio, this doesn't affect the FM band. Your radio instruction book should mention the process.

You could try an "inline" antenna booster, this is a small device that attaches inline to the aerial cable and radio and is powered from the +12 volt vehicle system, but these devices don't really give good performance unless a reasonable signal is present.

Aerial installations do require the underside of the panel they are mounted on to be clean metal (to make a good earth point) this is neccessary when really chasing best signal.
A recessing antenna can also be problematic when chasing better reception, the standard original simple external cowl mount type is generally better.

It is a nuisance when this problem presents itself isn't it, on one of my vehicles I used for long distance travel, I actually went to a lot of trouble to source a specific "high sensitive" radio and had a large fibreglass whip antenna to help overcome the problem.

Others will have different ideas.

Cheers, qldit.