I put new tires on and lost my handling also.
1. Your tire dealership most likely filled the fronts up to 80.
Take some of the air out. I run mine at 70. Big difference.
80 is the suggested MAX it is not an end all be all pressure.
2. I put on the most expensive tires thinking more money would net me more safety and better handling. Wrong.
The tires treads are too aggressive and the outer tread flexes and you now own a MH that is all over the road. :(
Go out and take 2 fingers on the outer tread and see if you can easily move it back and forth. If you can there's your problem.
Just visualize a heavy truck running down the road with that outer tread flexing all over the place....as one semi-truck dealership pointed out to me is why semi's run with tires that have the outer tread flat like a slick.
I'm STILL mad at myself that I put new tires on my MH.