You really need to tune the vacuum system to firm up the shifts on the SD. The stock settings are way too soft for most of us.

There's plenty of info in the archives about that adjustment, provided that you've got a Mityvac.

After you've done suitable research, you can repost on this thread and I'll help you with it if you get stuck.

Additionally, the 300 turbo benefits from the elimination of all lines to and from the black box. This is also detailed in the archives by me.