Jon,
Are you talking about the W8TVC/145.27 Traverse City repeater? Or any of the others? If so, you are on the fringes of the coverage area.
Take a look at the coverage maps from <https://kf8kk.com/wi0ok/repeaters.htm> to see.
Also you can go to <http://www.artscipub.com/repeaters/local/index.asp?state=michigan&city=BEULAH> and do a distance search but you need to join the group to look farther than 10 miles.
Do a search on "ham repeaters" near your area, or just the city you want to hit. Then get a coverage map and see whether you sit in the "Zone".
You also have a rise to about 1000 feet between you and Traverse City. Do a linear "walk" on Google Earth to see. You probably need either: a teller mast (hard to do, it's my problem too), or, easier, a 2M Yagi for directions gain. Your omni isn't going to put the signal/power where you need it to go.
Yes, take the 857 mobile (or even just portable) to a point maybe 1/4 of the distance closer to the intended repeater. Just a mag-mount antenna will be enough. If you can hit it cleanly, look at your antenna system. More RF power probably will not help in any consistent way.
GL,
Mac/WT4BT
