7427 4L60E 1st Gear Fuel Cut Off????

I've had one nagging issue with my 7427 MAF, 4L60E equipped 86 C10, it will not rev past ~4800 rpm, or exactly 35 MPH in first gear. It acts like it hits a fuel cut off barrier. Every "Fuel Cut Off" I can find in the parameter tree that is RPM related is set to 5500. I swore I found a 4L60E 1st gear parameter the other night that was fuel cut off related that was set at 35MPH, but I either dreamed it, or was drinking, because I haven't found anything like that again. I'm using the standard v251.xdf file to look at the 4L60E parameters. It doesn't shift into 2nd, it just hits the wall and starts doing an off/on surge, but it will not go beyond 35MPH in first. I haven't wound it out in 2nd to see if it repeats in that gear. I never hit a fuel cutoff in Drive due to the C10's aero dynamics, the 305 doesn't have the steam to pull much past 4000, and by that time the speedometer has gone past the 85MPH it stops at.

I was planning on swapping the 3.42s out for 3.73s or 4.10s, but would like to find this issue first before really impacting the trucks ability to wind out.
Thanks

The forced upshift/speed limit is to protect the planetary gears in the transmissions, 1st gear is 3.06:1 ratio so 4,800 rpm x 3.06 is about 15,000 rpms that the planetary is spinning...... The parameter you're looking for is MPH forced upshift 1 to 2, it will not shift into 2nd when in manually selected 1st but it won't go faster either. But I seriously recommend not changing it...... You'd probably be better off with a straight-cut gear manual shift powerglide if you want long 1st gear pulls.
Attachment 14241

Attachment 14242

Thanks for the knowledge. Was just surprised that it wouldn't pull past 4800 in 1st gear, but it didn't upshift. The reason I have a 4L60E in the truck now is because the planetary let go in the 700R4 that was in the truck. My tranny builder said it was due to a poor quality replacement part...but now I wonder.
Thanks again.
/r
Jim