Apologies in advance if I sound like I am teaching you to suck eggs, but...

You should really get the car checked over by a pro, tinkering with boost setup on a cossie is a big no no, unless you can check fuelling, etc... properly.
Drive it gently and get it checked out if you don't want it to blow up on you

PS: Can't remember which, but some yokohama tyres are useless on cossies, might explain your constant wheelspin - or, the road were wet