Transmission slips after sitting for nearly a year

[Dmcinfo]

I've been working on my Blazer for nearly a year so it's been sitting and not driven. I finally got it mostly back together and fired it up last weekend and decided to drive it around the block. I checked the transmission fluid level before leaving the garage and it was very low (selector shaft seal went bad when sitting). I filled it up but the transmission slipped a lot when I took my drive. The transmission shifted and drove fine before I started my restoration. Anyone have any suggestions on what to check or any explanation on why its slipping?

Thanks for any help.
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[Tom Vogel]

You might want to double check the fluid level.

[cleszkie]

Don't mean to insult your intelligence. But did you check the fluid level with engine warm and running in park? if not, you will not have gotten the correct fluid level reading and you may not have added enough ATF.