Frequently I lose the gps signal sometimes in rural areas, but often in cities.
even in areas without tall buildings. This makes the tomtom very unreliable, almost to the point of just buying a city map for each place I visit.

 

I have heard that some windshields are coated with a reflective glaze that will reduce signal strength. Have you tried it in a different car?

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bob

TomTom 730T
App: 8.351 OS:315187
GPS: 1.20 Boot: 5.5120
Map: North_America_2GB v850.2781
TT Home 2.7.5.2014
Gamin 660 (Sold)
Magellan 4040 (Sold)
HP iPAQ 310 (Thinking of selling it)

 

Could well be the OP's problem. Here's a couple of articles that came out just as the problem started to be "officially" identified:

Garmin Confirms Coated Windshields Can Block GPS Reception (GPSmagazine.com)

The problem isn't confined the just the manufacturers mentioned in that article, either. Saab and BMW have also had issues due to windshield materials and construction. Also noted, some 3rd party window tinting materials (not even legal on a windshield anywhere I know, but some peoples' kids, right?) will hammer the signal badly.

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TT720 - NC 8.351 - NA2GB 850