Odd 1-2 shift - 4L60E
 

I put my truck back to stock and bought a used 4L60E (stock except for a billet shift servo) locally with around 70k miles on it. It seems to work great except for the 1-2 shift.

When shifting under light throttle (~15%) it will hesitate to go into 2nd. I can feel two distinct "clunks" as it shifts into 2nd. They are not very firm clunks by any means, but subtle, feels like two shifts almost. I'm guessing something is slow to engage.

If I give it very light throttle it will not do this, nor under heavier throttle. It also only does it when warm. It will not do it in tow/haul mode either.

I'm thinking since it only does it at a certain TPS that I can help reduce this via tuning. Anyone what what I should try adjusting first? I'm thinking line pressure to start.

The tune is currently 100% stock transmission-wise.