For the 4r70w it is called a(valve body plat kit).
It will firm up the shifts but that is part of how it helps the tranny.
Quicker firmer shifts produce less friction and heat then the slow sloppy shifts that are common with the factory set up. Less heat = longer life of the trans.
There is information on this site on how you can change the springs around or something like that in order to adjust the shift firmness so it's not uncomfortable for DDs.
Mike sells one for 100 bucks and it's the one most go with.
Scroll down to transmissions.
http://www.madenterprise.com/catalog/F150.asp
He also sells an installation kit for the blower intake assembly off the Lightning.(for the conversion).
http://www.madenterprise.com/catalog/scparts.htm
Phil
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Built Lightning block.
Stage 3 Ported heads. high performance Cams
Kenne Bell L upgrade blower 16 PSI
DMR Cog belt system
Kooks long tube headers
BTS race built 4R100 tranny
100 shot of nitrous
best 1/4 to date.
60' 1.68
11.76 @ 116.17