I bought FLT level 5 4L80e with about 1500 miles on it...
Will not shift 1st to 2nd under full throttle.
I really never got to test how 2-3 rd was holding.

It was working fine in previous truck - Crew Cab forged 5.7, turbo 12 psi.
I installed it in my truck (408, 12-13psi), drove around dialling in tune and shifted fine under part throttle and the transmision was the least of my worries. I never went full throttle shifts though, tires would just go up in smoke. Finished tune doing 2nd GEAR pulls and 3rd GEAR pulls - I would just easy into throttle and made full pull.

Finally made it to the track on slicks -

1st pass bumped rev limiter (6900rpm) then shifted, comanded shift was 6350rpm.

2nd pass slight bump on rev limiter (7000) and comanded shift 6000 rpm.

3rd pass - no longer shifting into 2nd unless i completely lifted off throttle..

I made about 4 more passes trying everything I could in tune to make it shift and nothing. My logs show where 2 nd gear was comanded, just not happening. I changed out the speed sensors form another truck that was there and still nothing. I decided to test truck in parking lot under part throttle, 1st, then 2nd gear felt funny - like if it was in a bind at first then fully shifted, 3rd gear went in then neutralized then 3 rd caught again. After this I deciced to load on trailer. One of the trucks that was with us ended up braking an axle, loaded it on my trailer and drove my truck, about 35 miles. Did fine but babied it.

Any ideas what the issue might be? I called FLT and was told to check tune, myself and a very reputable tuner messed with it and never made it shift.

I had locally built 80e before with no issues, I only went to this for the billet input shaft, I plan on installing trans brake down the road. And I figured this was a better unit.

 

what does the fluid look like?

do you have a temp guage on it?

 

The fluid looks good, I plan on pulling pan off tonight.
Temps stayed under 180 while tunning and never got above 170 at track

 

How many quarts of fluid did it take to fill when u did the swap?

 

I would look very closely for debris in the pan when you drop it.

How was the trans tuned and treated before you got your hands on it? I've seen a lot of even well built transmissions die an early death because of improper break-in or tuning.

When Somethings been behind a stout powerplant in a heavy vehicle mileage is kinda subjective...

 

Fluid level was good.. Not my first rodeo.. Lol

 

The tune on the other truck, was done by the same guy that's was looking at the tune on mine with me...
I really think this is internal, but what? I am not a trans guru..

 

What about requested mph? I know when I was tuning my 60e requested RPM was not the only thing that needed to be addressed. If I went fron a requested 2-3 shift at 76mph to say 74 mph it would shift sooner ....make sure this isn't being over looked

 

Try putting some shift time if you zeroed it out. I had one truck not shift cause of that.

 

Shifts commanded at 30 mph and 5000 rpm... We looked at every thing