After 5 miles or so my arms get really stiff and I pretty much have to lock my arms to reach the bars.
Do you mean
After 5 miles or so my arms get really stiff and THEN I pretty much have to lock my arms to reach the bars.
Or
After 5 miles or so my arms get really stiff. And I ALWAYS, EVEN BEFORE THEN, pretty much have to lock my arms to reach the bars.
Because there's a big difference.
And try reading this:
Learn About Bikes with Rivendell Bicycle Works