Try resetting the decoder. If that solves the problem then try changing the start voltage. It might be worth an extra minute to re-read those instructions first--it possible you missed something the first time around.
If that doesn't work it is over my pay grade.
Sounds like you changed CV29 and not CV2. You now have the decoder set for 14 speed steps.
Reset it (CV8=8) and then reset your address and make sure you program CV2 for start voltage.
--Randy
Modeling the Reading Railroad in the 1950's
Visit my web site at www.readingeastpenn.com for construction updates, DCC Info, and more.