Agree based on my experience of running a ZJ with a 242 for 15 years. It's possible your 249 was binding up in turns and that may have lowered your mpg. I have tried running my ZJ in both 2wd and full time and there really is no difference in mpg. The nice thing about the 242, is flexibility. If you have a bad winter, you can leave it in full time. To reduce wear and tear you can run in 2 WD. Off road 4x4, part time works great, no waiting for auto engagement like other systems. One improvement I could have suggested was a Torsen differential to provide auto lock up in full time. Overall, the 242 is a great case for people who don't mind shifting for themselves.
2007 WK Limited Hemi QDII
1998 ZJ Laredo 4.0 Selectrac