Alternator charging advice

I have been having a charging issue. I have underdrive pulleys on the car and at idle I was getting 10.5 volts and when running the car it would go up to 13.5 volts. Problem is I couldn't drive at night with the lights on while at a stop light.
I changed the alt pulley from a 3 1/2 to a 2 1/2 and now at idle it is 12.5 volts and when I rev the engine it jumps to 16 volts and higher. I really can't afford to change all the pulleys if that is my problem.
Any advice. I have checked the alt and voltage reg and both are good.
Thanks
AL