Trans works great besides when you put it in reverse it takes 4 seconds to kick into reverse.

 

Your thread says "99f350 rebuilt". If it was actually the tranny you had rebuilt something isn't right and I would bring it back to them. It sounds like it is slipping. JMO

 

Have you checked the fluid level? Low fluid (especially when cold), can cause this delay. On the scary end of it, reverse is usually the first to go when the trans is on its way out. If its under warranty, have them look it over.