TF727 issues

strange issue with our rebuilt TF727.

At first it engaged and drove up and down the driveway perfect.

Today I was making some carb adjustments, and backed it outside to mess with it.

It’s running great.

But.

When I went to pull it back in, I put it in gear, gave it some gas, and that’s where it gets bad.

It acted like it went into neutral for a split second. Reved up about 400 rpm and than bangs into gear.

If your already rolling, and give it gas it’s fine. But from a dead stop it flashes than bangs into gear.

Does this in all gear selector positions.

Any help is appreciated. Thanks. Eric