I haven't tried the Sea foam, but many people have had good results with it. I can confidently reccomend one of the "gas additives"...Chevron Techron. Add one can to a tankful, and do it for 2 consecutive tankfuls. It will clean everything whistle clean. After it's run through the system, change the oil, and you can start re-tuning the fuel. Don't try to tune with the Chevron in, the car will get more knock than with premium (can't explain that though, other than it may lower the octane).
I had bad carbon build up on a previous car that I found when gasket matching the intake manifold. There was carbon on the intake valves up to 1/2" thick! I put it back together, and ran the Chevron, took off the intake and it was completely clean. On the GTP, I've been dumping in a can before each oil change, at 80,000 miles I had the injectors flowed. They checked out within 1% of each other right off the car before professional cleaning. If you use the Chevron, they make 2 different kinds. Use the one that has the intake valve cleaner in it.