Any Tips for Imporvement on a 4R70W?

[dylanCamaro582]

I have a 4R70W in my Mark VIII and I'd like to improve its perfromance, but it slips in 1st and 2nd when cold and just womdering should i worry about this?

I was think about installing a Shift kit to help improve perfromance and is there any thing elese that i should look at, and I doing it on a College Student's budget.
By the Way, My Mark VIII is stock.

P.S. I know my sig say otherwise.