Having a fair about of two-way telemetry experience (esp from satellites), I can comment on the speed problem, but not the hr. There are a couple of things that might have happened...

You may have had a weak signal at one point during your ride which resulted in a rouge data point in your file. This will cause the max speed to be off... This point could be anywhere in your file... When you map it, do any rouge points show up - long or jerky lines? I sometimes have to find said points and just edit them out of the file, then your max speed should be ok. Sometimes those points are are also at the very beginning or end, if you accidentally start and/or stop your timer or forget to reset. This is a potential problem with any gps unit. hth...

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Don't hold back

Powerlines or electrically "noisy" stores that you ride by (maybe Radio Shack for example that have lots of TV's going and stuff) can cause the HR to jump around. THere is a hilly road I ride where the power lines are low slung, and my Polar regular freaks out when I ride too close...

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I did have some rogue points or spikes with the speed. I reset the HR today and went for a run today with my max HR only 180 so it appeared to work. Still have problems picking up satellites running on a 3k road along the base of a hill. There is some overhead cover from trees, but didn't get any pace info for the 90 minutes I ran. Does weather or cloud cover affect the signal strength or just buildings?

Barefoot

Nah, normal everyday cloud cover shouldn't really affect it. Some of the more important aspects with regard to accuracy are:

The number of satellites visible (i.e., if you are next to a hill or trees you may be getting fewer satellites). The loss or flickering (trees) of only one key satellite can cause a 50 meter error. This is likely your problem.

Satellite geometry (i.e., wider angles are better for accuracy, but worse for their propensity for getting blocked by things like trees and hills as well as being affected by ionosphere and troposphere). http://science.nasa.gov/...ack/3d/JTrack3D.html

Signal multipath (i.e., the signal is reflected off a hill or building causing errors).

Sunspots - We had a fairly sizable event on May 14th which could have certainly caused erratic behavoir. http://www.spaceweather.com/

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Don't hold back