I don't know whether we have to label that as a zenkai, but it is highly implied Goku got an increase after 22nd TB. Roshi was stated to be not
far behind Tenshinhan, yet he made a big deal out of his younger self's power. In other words...
22nd TB Roshi<=22nd TB Tenshinhan<=22nd TB Goku<Young Roshi<Mutaito<Post 22nd TB Goku