I have a stock 02 t/a ls1, auto m4

im sure that u guys have did this maybe, maybe not...one i get up to speed to run it all out....i get to 150-155mph tachin 5800rpm....the thing is that this seems to be in third gear...couting the gears up to 150mph it never leaves third...is the 4th gear just a cruising passing gear...once i get out of it..it will keep into 4th but stays in third on up to 157 the fastest its been, and about all the rev limiter will allow

just wondering if any others are like that..and was curious...