Turbo 350 lock up?

[ed scholter]

Been using GM turbo 350's for 30 years. Today I had a first! Floored it to get passing gear and when I let it up it stayed in 2nd gear. Got off the hi-way and slowed down it then shifted to first and stayed there. So I drove the last 4 miles in first. I finally shut down and when I restarted all was well. Question is, What spool piece hung up??

 

[6.2 turbo]

Could be the governor sticking. A none working modulator will still allow upshifts,but later,like 4000 rpms. I never connect any of my th350 kickdown cables.