What are your SWR readings on channels 1 and 40? They are probably both over 3:1, but knowing which is higher will tell you which way to go.
I have always remembered it this way:
Channel 1 tells you which way your antenna needs to go. I.e., if your SWR on channel 1 is higher than on 40, the antenna needs to "go up," or, rather, be longer. If 1 is lower than 40, the antenna needs to "go down," or, rather, be shorter.
2013 Billet Silver JKU Sport S, 6-Speed, TF Leveling Kit, Spidertrax 1.5" Spacers, 285/70R17 Firestone Destination M/Ts on OEM Sport wheels.