Re: 5 to 6 speed conversion
The suncoast kits are designed for the duramax. The valve body would work, but the tcm would be all wrong. They MIGHT be able to make a TCM for a gasser, but personally, I wouldn't touch one of their 6 speed conversion tcms with a 10 foot pole.
If you have a 03+, are mechanically and a little electronically savvy and have some patience, you could probably get a 6 speed transmission, body harness and TCM for less than their TCM. IIRC, I paid less than 1k for my 6speed trans and was able to more than recoup that when I sold my freshly rebuilt 5 speed.
If you have a duramax, IMO, the ONLY way to do it is to completely convert to a lbz/ 6 speed as I did. If you have an 03+, its largely plug and play. 01-02 not so much. That way you get all the 6speed benefits (including tap shift and the enhanced winter warmup idle which works much better than the 04 lly winter warmup idle) and a stock, not butchered TCM.