I have had a similar problem with my Isp and may have a solution to your problem. Some Isp's like to throttle there connections by setting a lower MTU allowance. The average package size is set to 1500 MTU. Your Isp may have assigned a lower package size on the udp. To get around this problem you have to set the MTU size to 1300 on the tap adapter. On windows you would do the following:
Go to your tap-32 adapter, open properties,open configure,open advanced, highlight MTU and put in a value of 1300.
Press okay and try connection.
On Mac, you go to system preference, select the network interface you use to connect to the Internet, press the advanced button, then click on the hardware tab. There you will see the Mtu and put in the value of 1300.
I hope this solves your problem, if not it may be useful to others.