I'm afraid there is no definitive "correct" figure for Total Ascent - every application calculates it differently, so you can't compare figures from different sources. We've looked into this at this a lot in the past (see this thread for past discussions on the topic) and have realised that we'll be constantly chasing our tail if we try to match calculations from other sources. The best advice we can give is to only compare ascent calculations from plotaroute with those of other routes mapped on plotaroute, rather than with figures obtained elsewhere - what is important is how figures from the same source relate to each other.
I have the same route mapped with plotaroute and ridewithgpa, and there is a big difference in the climbing (elevation). Plotaroute says 3031/ft and ridewithgps says 2136/ft. Why the difference and which is correct?