Sorefingers,

From the circumstances you describe, the first question I'd ask is: Are you sure the strings are going dead, or are you just not used to the muted sound you get compared to what you heard when you were using picks?

The second question would be: Do your hands sweat a lot when you're playing?

I'd guess the first might be a large part of the problem, but if you're adding sweat from a picking hand (which wouldn't be on the strings if you're using a pick) to the mix you might be getting some extra deadening.

Don't know the specific strings you mention, but I've always found Martin strings very heavy on the base and very thin in the treble. I know their gauges tend to run to extremes in comparison with other strings. You might be looking for a more balanced set. I've been using D'Addario phosphor bronze for a long time and I'm really happy with the results.

cheers,

david