Re: Tsuki Iriminage - Step back hand grab
Do the technique very slow, over and over again. It will take time to get the body mechanics ingrained so just be patient.
From your description, after you grab uke's hand, I would use your hips to swing your right hand over to the right. This should help get uke off balance by twisting his/her body, protect you from a left punch, and get uke's right hand out of the way so that you have room to now safely step into the rear of uke with your left foot. Keep the momentum going as you slip into tenkan. You can either let go of uke's right hand or keep holding it until it is time to throw with the typical iriminage arm, personal choice.
Some techniques you will never find on video or ever have a name for. They are personal techniques of the Sensei. I have a new dvd of Yamada Sensei of the USAF and he stated the fact that some of the techniques he will show have no name and are his personal techniques. Something he made up and likes to do.