99 tahoe braking problem

I have a 99 tahoe 4wd, a few months ago the brakes became soft so when braking at high speeds they seem fine, but when stopping at a red light or braking at slow speeds the pedal goes to the floor and the abs kicks in. I just changed the front pads, rotors, calipers, caliper bolts/sleeves ( I greased the sleeves,hope your supposed to!) and changed the fluid and bled all four brakes. Still have the same problems when coming to complete stop with the abs kicking in. Any suggestions??
thanks

Probably the master cylinder, if the brake pedal goes to the floor.

You need to bleed your brakes about 4 times...pedal is stronger!

I was thinking the master cylinder also...is this something a semi intelligent mechanic can do or should I take it to a garage?? any special tools needed?
thanks

It's not hard to change, but you will have to bleed the brakes again, after you change it.