I bought the SLK thinking it would be the budget way to get throught the SA series. It isn't. You'll need to add Full racing suspension, Sport Brakes, Racing Muffler, port polish, Chip, Full racing Tranny, Medium Slicks, Lightweight 1&2 and the obligatory oil change. Here's were mine ended up:
F/D: 4.500
A/S: 23
LSD: 15/35/25
Springs: 6.6/5.8
Ride Ht: 94/96
Bound: 4/6
Rebound: 5/9
Camber: 3.0/1.0
Swaybars: 3/4
Let it be said I don't much like this car. I'd recommend getting a stock CLK, adding T4 medium slicks, and trying that. PLus, you're going to win an SLK anyway.
For the TT, try this. It should blow away the Beginner races, and win the Amateur ones with good driving.
Medium Slicks
Sport Brakes
Lightweight 1 & 2
Variable Center Differential (VCD)
Port & Polish
Turbo 2
You may want to add a muffler/intake instead of the brake upgrade. If you add the race suspension, here's a reasonable setup:
F/D: 4.433
A/S: 24
Springs: 9.0/6.6
Ride Ht: 100/100
Bound: 3/4
Rebound: 7/8
Toe: +0.5/-0.5
Camber: 3.0/1.0
Swaybars: 3/6
I really like the TT when it is set up this way. Good luck and hope this helps. Welcome to GTP!