i took the carpet out of my parts truck and didn take the dash out. you have to remember that a 15 year old truck has alot of miles on the carpet and some could be melted underneath thus holding you to the floor. good luck
just cut the carpet right there as far back as you can with a razor, when building a car the carpet is one of the first interior panels so eerything surrounds it.
im pretty sure that its your heater core holding the carpet in place, as stated jsut cut around it, thats what i did, you will never notice it up there especially once the radio housing is back in