Speedo 15mph off. Dealer could not fix, Lol

[97e350]

I have a 97 E-350 that was born as a gas van with a 2002 7.3 transplant. I did not realize this untill AFTER I bought it... ( Good commercial for car fax, Lol) They did a pretty ****ty job and it has been nickle and diming me to death, In money and time.

The speedometer is reading 15mph slower at 75mph. The van has 3.55 rear so I'm thinking maby the 7.3 computer was programed for 4.10. I took it to the dealer yesterday for a alignment and to re-cal the speedo. They said the closest they can get it is 4mph under. But I guess no one test drove it because it is the same as I brought it in, 15 under. ($70.00 later) And this was the Head Master Tech ???? And the alignment is off and pulls to the left. I thought it was easy as putting the revs per mile of your tires in the abs module.

So should my computer be able to be recaled in the abs module by ford? or any other way. Since the speedo is so off, is it effecting my shift points and milage? Would it be bad to drive like this?

Thanks

[rickwa]

Speedometer Repair, Repair Speedometers &* Instrument Cluster Repair - Advanced Auto Electronics, Inc. advanced auto electronics. I bought a rebuild speedo from them. they should be able to help. they are very good