I have no reverse

Does it slam into reverse when you rev it up or just not want to go until you give it fuel? When I bought my pickup it wouldn't engage into reverse until I accelerated and then it (somewhat violently) engaged and reversed quickly. It was hard to back up just an inch. I replaced the transmission fluid, filter and adjusted the rear and front kick-down bands with an in-lb torque wrench and that took care of it. The fluid and the transmission pan looked neglected and took a while to clean. I am not sure if the right transmission fluid was even in there! I saw an empty quart of Mercon under the seat that made me extremely nervous.