Shift Kit Help

Hey to all, im new to the whole mustang forums. My problem is the following.
I own a 01 GT with a trans go shift kit that i just installed about a month ago, now my 1-2 shift is soft and long, i noticed that a fuse blew that controlled the overdrive. the rest of the shfits are firm and clean. Will Low/High ATF cause this, and also what is the proper way to check the ATF with car on or off, hot or cold in park or netrual???

Thanks to all.

i used Mecron V fluid, was that correct