I am not sure if it is slipping or not. It seems i have had this problem before but as of late it has gotten worse. It shifts and seems fine but when i am going up a hill it bucks and seems like its slipping. The engine rpm doesn't change either i have replaced the iac valve already also. As for the transmission fluid it is full and has a little bit of a dirty color to it. I am not really sure what is wrong with my truck please help.