I've got 2 vehicles with 700r4's, my '87 Formula and my '92 K1500 Blazer and both just developed the same exact problem that appears to be weather related.

Both have done this a few times and it only happens when it's sat for a couple of days and I start it up when it's in the teens or colder out. I make it to the end of the street (they shift fine from the house till they start acting up), make my first left hand turn (maybe ¼ mile, at most) and accelerating away they suddenly feel like they were just shifted in neutral, you can rev the engine and nothing happens. I believe (I'm not positive, it's rare enough that I'm never paying attention when it happens) that it's shifting out of first and not shifting into second. Every time with the truck I've managed to shift it into N and then when I put it into OD again it's fine, and doesn’t do it again. In the formula the couple of times it's happened it freewheeled for a second or so and then engaged the gear hard and again, shifted normally from then on.

Besides the dissimilar vehicles, the truck hasn’t had any changes besides a big oil cooler added; the Formula has a Transgo shift improver kit installed. Both are filled with relatively fresh Mobil 1 ATF (less then 5K miles on both), the formula has about half the mileage of the truck.

 

Valves are sticking. Could be one of the boost valves in the pump. Just pull the pan to get to them. Or you've got problems with the 2nd servo sticking.

Try manually shifting it. When you know it's going to do it. Mine did something similar but not near as bad at 40*f.
You might check the oil level too.

 

So can anything be done for them not to stick? Why is it only happening when it's really cold?

 

probably because of the fluid being thicker when cold, mine doesnt act top funny, but i dont push it hard either when first getting into it in the morning.

need a tranny warmer

 

I need to spend more time futzing with these trannys like I need a hole in the head.

The only 700r4 that I've ever owned that I've been happy with is the one that was in my '83 TA, which was basically factory and supposedly one of the worst ones out there (supposedly valve body problems and it used the smaller, early 27spline converter). That one did what I told it to, when I told it to do it.

The one in my truck hasn't done anything really wrong (besides this), but I feel it shifts late and occasionally throws a shift that's just not right (at the wrong time or just doesn't feel like a nice shift). The one in the formula use to slip the 2-3 shift when I bought it. I added the transgo shift kit and now it works absolutely beautifully on the street, but does weird stuff at the track (on the 1-2 shift the car actually noses down, like I hit the brakes for a second during the shift, doesn't do it on the street. I think probuilt suggested to run an extra ½ - 1 quart in the tranny at the track but I haven't had a chance to see if that helps or not). It also seems to react to moving the shift lever from one gear to the next slowely (I have to move the shift lever at around 4000 to get it to shift at 4700rpm), but again, only at the track

As far as I'm concerned, trannys are supposed to just shift crisply when you tell them to, none of the BS that it seems that most 700r4's do. I'm debating whether I should spend the time to just learn to build them to do what I want them to do or just forget the whole idea of OD and convert to a TH350 or 400 (I'd love to run a 4L80 in both vehicles (the truck does a lot of towing, the formula will soon make more torque then I'll know what to do with), but I can't see spending over $2K on a tranny).