When it comes to unlimited-performance, we-dare-you-to-break-'em T/C's there are four main options; ATS, DTT, Goerend Brothers, and Suncoast.
A lot of guys swear by
Goerend Brothers; they have a cult following amongst the Diesel community, have the best prices for unlimited-performance T/C's, the best customer service, and a great warranty.
I got my convertor from them for $550, and it was $100 for the additional life-time warranty.
ATS are the Banks Performance of transmissions; they've been around forever and there was a time that they were the Caddies, but they're way expensive and have been having warranty problems recently. And they might not even make non-lock-ups, I don't remember.
DTT and Suncoast are both really good products too, but they're both a couple hundred more than Goerends'.
The step down from the big four is a Hughes for around $400, which is supposed to be a good unit for mild ~400 HP builds. But I've never actually heard anybody who had one first hand, so the "Hughes is a good T/C for ~400 HP builds" bit of information is kind of getting dated at this point.
And on second look that gauge I posted isn't a Z-series... The website I stole the picture from was mis-labelled.
This is a Z-series...
1990 D-250 Regular Cab: Tweaked injection pump, built transmission, a cataclysmic charlie foxtrot of electronics, the most intense street-ran water injection system in the country, and some more unique stuff.