The Red, Black, White wires in the entry box are all connected to a standard 3-way switch? YES
Are these three wires in the same cable? YES
I dont know where the 3 wire cable from the entry runs; either to the fixtures or garage gang box ?????
I can measure voltage on various wires
In answer to oberkc:
The garage is 3 gang box with 3 swithces : the 3 way that is the issue, another single pole controling a ceiling light in garage bay 1 and another single pole switch controling ceiling lighting in bay 2 and 3.
Garage box has 5 cables coming in:
Cable 1 is 2 wire blk/white (blk goes to dark colored screw on 3 way switch) (white to Neutrals)
Cable 2 is 3 wire blk/white/red (blk and white to 3 way switch) (red to wirenut with all blacks)
Cable 3 is 2 wire blk/white (blk to single pole switch) white to neutrals
Cable 4 is 3 wire blk/white/red (blk to other wire nutted blks as well as red from cable 2
Cable 5 is 2 wire blk/white (blk to wire nutted blk) white to neutrals
I hope I have all the details !! thank you!