I saw an episode of shadetree mechanic several years ago where they attached cannisters to the fuel system and cleaned the throttle body. Do you know if there is a kit available for the 1998 GP 3.8 series II engine and is it advisable to try this as a DIY job? Also where can I obtain this kit?

It would be effective if you have the old TBI type system where the fuel injectors are located inside the TBI but on a multiport fuel injected system ineffective. All you will clean are the fuel injectors.

You can use either GM Top Engine cleaner or Sea Foam to clean the throttle body while the engine is running. The stuff is fed in via a vacuum line port.

The best way to clean the throttle body on a SII 3800 engine is manually with TB spray cleaner with the TB left installed or removed. The IAC will need to be removed and the seat cleaned separately. The MAF sensor should be removed so the TB cleaner does not damage it. Only cleaners like CRC MAF spray cleaner should be used to clean the MAF.