4L60E shudders before downshift

my 1993 K1500 5.7 L-- when going up a gentle grade at about 50mph, just before the first downshift [I presume this is when the converter unlocks], I feel a shudder that lasts for a couple of seconds. If you give it slightly more throttle it shifts and no more problem. I assume the lockup clutches in the converter could be slipping under load, but have no experience with this.

This can also be a misfire when the engine is under load, then when tcc is unlocked the miss goes away, I would look at that possibility first.

What do you think would be a possibility for this missfire? My truck does the same thing. It's like the timing goes out of wack, then it downshifts and it is fine again. Could Map sensor be the problem?