On my 1997 Lumina, it seems the t-stat might be stuck open. Never reaches full temperature. It looks to me like you have to remove the exhaust manifold to get the t-stat out, is this right or am I looking in the wrong place.

no you dont. Aut worst you will have to remove the throttle body, and use a 13mm wrench (i believe) to get the two bolts out.

You can get it out without removing the t-body or crossover pipe, but you'll have to bend your wrist in angles formerly unimaginable. That's how I did it.