D100 SLANT6 3SPEED TREE CONVERTED 4SPEED

I have a d100 tha had a 3 speed on the tree which I convereted 4 on the floor. I put 2 diff 3 speeds and now the 4 speed happy with the swap but getting the same problem. The speedo seems to be 5-10 miles off between 25-35 and once it hits 50-55 I have no clue how fast I am going.
Thanks
Author: KLPDAFFY