To much pressure, When I first started out 2 years ago I did the same played and got tired very quickly I was just putting to much pressure on my fret hand, You will gradually find yourself easing off as you progress it just takes as with everything a bit of time.
Redo all the sections, Delete all that are currently there and reapply them the tab may have had its own section markers when importing it and is quite a ball ache.
Erm... this always gets me into trouble with the old folk who learned the hard way. It got me to try and learn guitar now after 1yr and a half, I can see why someone who has never learned with it would say its stupid but for me it made playing a guitar easy to learn (take that with a pince of salt), I can do without it now and just go with the flow if any thing stops me playing I'll just slow it down a bit and see whats where.
Adding DD is a fucking 10 second step in the toolkit for the creator, Its a 5 min step for someone who downloaded it work it out for fuck sake it no 2 second job for someone who doesn't even know how to use the toolkit and for those who say if you can't play it why create it, I made a song I cannot play and it seems to be one of my best pieces of work (except for the tone :???:) so you cant say if you can't play then dont make it thats not what RS is about I am afraid.