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Yeah, it's a head scratcher. Thanks for taking an interest, I'll keep an eye out for anything you might post on it down the road. Summer's coming, the problem will likely hibernate!

Mike

well that certainly is a good question.  My first thought is trans temps not being hot enough until after the vehicle runs for that 30min. 

If for some reason that is the cause my next guess without having the vehicle here would be wiring from the PCM-Trans could be damaged internally and while driving the wires are being moved slightly causing surging of the TQ convertor.  The problem with this theory is that temp should not play into this so the 30 minutes it takes for things to work properly should not have any effect on the wiring.

I wish that I could be of more help on this and I will continue to look for a reasoning for this as I love to solve problems like this.  Unfortunately at this time I just dont have a solution.

I had this problem posted @ ChevyMalibuForum.com, a fella who goes by the name Malibu Glow suggested I toss it over here as he thinks "Mark" is the man for  this.
98 Malibu, 3.1, 4T40E trans. When temperatures are cold, car is cold, the TC doesn't go into lockup, as is correct. As the car warms up, it starts locking & unlocking the TC, cycling in & out more rapidly until after 30 min or so of driving, it works properly. What i've looked at:
Trans fluid level - good
Lockup (TTC) solenoid: 11 ohm where 11-17 is the spec
Shift sol A: 21.7 on 20-40 spec
Shift sol B: 21.1 on 20-40 spec
EPC 4.3 on 3.5-4.6 spec
TOT (Trans temp sensor) ohms out as in spec at every oil temp interval listed up to 170°
I tied into the TTC PWM SOL wire and can see that when the TC cycles in & out, the signal is in & out, so it is a command. I guess.
No check engine light. Checked with scanner, no codes, no pending codes. Was able to monitor trans oil temp, engine coolant temp via scanner, temps were stable.

Sure seems to be a temperature issue. I guess that's why the guy sold it in the summer. :-)
Any ideas out there?