I just did my first rebuild on a tranny and I got it in my car. If I put it in D it will go just fine but in L or reverse the engine boggs down like it going in gear but it wont move. Any suggestions ? Do i need to adjust the bands? Its a 1964 Mercury Montclair with a 390.

Does it shift in D position?

How did you adjust the bands?

It dosent feel like its shifting or slippping. I havent adjusted the bands at all. I just put them back in like I took them out.