It took me months to beat RE4 on pro, but I didn't use Gameshark.
The hardest part for me, ironically, was in Salazar's castle where you're with Ashley and you have to go to the opposite end of the room and turn a crank, then go back and have Ashley start turning some. By the time I got here, I had almost no ammo left and a think a couple of grenades... Ultimately I ended up getting past that part though and after that it was pretty much smooth sailing.
My favorite part by far is the military base because you get very little air support, so it gave me lots of time to perfect my skills with the S75, a gun that I used almost exclusively on RE4 anyway, so I'm already good with it. It's just more fun when you have all that pressure of taking down a military base by yourself with your rifle whilst your air support is more like moral support lol.
You should try it again without cheats, it's far more satisfying