We will need to know your JetPack model number before we can provide you any specific suggestions or steps.
From what you have provided so far it sounds like your device has a connection problem in a specific enviornment. The JetPack may have too much interferance or may not be compatible with the towers in that area.
The best thing to suggest for now would be the various levels of resets. In a nutshell you can try power cycling your Jetpack, unplug/replug your SIM card or restor the defaults by pressing the button under the back cover.
If those resets do not improve the problem the next best thing to would be to contact VZW when you are in the area with poor reception and see if they can confirm any outages or issues with the local towers.
The last line of defence would be to look into antennas and/or amplifiers to boost your reception. Normally a site survey is required before additional equiptment can be suggested. We need to know if there is a JetPack signal to connect to before we try to beef it up, otherwise more equiptment will do you no good.