I have a 2005 SLT1554,I bought it in sept 2005. It has 214 hours on it, the first two years, 50hrs were mowing a bumpy 1 acre lot, then in 2007 and 2008 it was used to mow a slightly bumpy4.25 acre lot. It overall has been an ok mower, here are the problems we have had..... The Weld broke on the front bumper @ 70 hrs, the parking brake button came loose at about 125 hrs, the front hood latch broke free from the hood at 170 hrs so now i have a bungee holding it shut,because the hood is cracked where it mounts. Thats about it for breakage.
The mower has a decent cut and it will mow, deep wet grass no problem, it has plenty of power for mowing, however on hills the mower struggles, the engine never bogs but the transmission seems to really struggle, so if you have inclines I would pass on it. The deck belt falls off on a regular basis, it is the original belt and is in good shape though. The motor Backfires sometimes when hot and you shut it off ( I have 2 other machines with similar kohlers and they both do the same thing).
And at 214 hours the steering is fairly loose but its not bad enough yet to warrant fixing it. However the mower has always started and it runs great.
This year I have bought a used JD 655 Z Trak with 1100 hours on it to mow my yard and have retired the 1554 to doing mowing along the fencerow and a few other areas and as a supplemental mower. I also started pulling my yard cart and sprayer with it. I tried pulling a 500lb lawn roller with it (Just about 15 feet out of curiosity) and Forget it, it is not meant to pull like that, I Use a Atv to pull the lawn roller. The motor seems capable of much more than the trans.
If I had to do it over again, I would say I might buy a 1554 if I didn't have much more than an acre to mow and I didn't have to pull much. I would say it is a cheaply made mower with a big engine and a big 54'' cut.