How do I know if I need to replace Honda transmission?

I have a 98 Honda accord and recently had the motor replaced. Husband says that the transmission is slipping. When we had it towed back to our house, the guy mentioned since it had no problem going in reverse without slipping, it might not need to be completely replaced (just his opinion). Looking for any kind of help. It is a 4 cyl.How do I know if I need to replace Honda transmission?Pull the transmission dip stick if the fluid is brown and has a burnt smell to it the trans is shot.