Started with 4.8 w/ M5 in reg cab 02. Wanted to upgrade to lq9 w/ t-56.

To start the conversion i found what i thought was a good deal on a t-56 from a 2000 ss. Had 60,000 on it. Well made the swap from M5 to t-56 and have low roar in transmission. I added some royal purple, tuned down the roar a little but now wanting to slip out of 1st. Want to know what could be causing both problems and to gain any future advice.
Should I go ahead and upgrade my t-56 now or what? Worried about it holding the power.
and what to do to upgrade. and if this is a good setup goals.

 

anyone.....