They were and are idiots for telling you that and installing the super-short SYE kit. It is for reasons like that I hate 4WP, few of their "techs" know WTF they are doing.
Well, you can no longer simply swap in a speedometer gear to calibrate your speedometer since a super-short SYE does not use a speedometer gear. That is why your speedometer is now way off. The only way to calibrate your speedometer now is by wiring in an external speedometer calibrator like from Truespeed or the Dakota Digital at Universal Speedometer Signal Interface