Zero Turn Mowers

I have a Z5426 (Husky) that I purchased new at Sears in 2008. We have had many issues with the mower (in fact sears has at their choice replaced almost everything on the mower except for the handles, wheels, and seat!). One lingering issue is the parking brake adjustment, it simply does not hold and the sears guys seem to think that it is okay. How do you adjust it?

also, they recently replaced the entire engine (still in their service agreement warranty and again by their choice). The new engine has a different linkage arrangement on the carburetor. The sears guy has disconnected the OEM choke cable and it is now all tied into the throttle cable. Now all the way forward on the throttle is choked? The problem is that we now do not get the right speeed out of the mower. According to GPS we only get about 5mph as oppose to the nearly 8 before. Should the controls have been changed along with the engine? or is this not the right engine?

Thanks for your help.