Have a 2004 GMC Sierra 1500 with a 4l60e. Transmission was replaced about 3 years ago and has less than 25k on it. Recently started having problems shifting into reverse. When going from park to reverse transmission will feel like its slipping, but if shifted into neutral after initially shifting into reverse, then back into reverse from neutral it feels fine, no slipping. Low line pressure? Reverse solenoid? Fluid is full. Any help would be great