I ordered a copy of the Tahoe-Yosemite Trail Guidebook from half.com after I got home and just took a look through it this morning. Apparently the TYT, although proposed by the Forest Service, has never been official, and even if you read old Sierra Club Bulletins, there wasn't much info on it, so the author (Thomas Winnett) wrote the guidebook to try and help the process along. The first edition was published in 1970, mine in 1987. The book describes (in a southbound direction) a 180-mile route from Meeks Bay on the western side of Lake Tahoe to Tuolumne Meadows, and my edition includes black, white, and blue topo maps of the whole route, likely the only ones you'd need to hike the trail.
Here are my thoughts on the route (arranged northbound):
From TM to Bond Pass near Dorothy Lake the TYT is the PCT, so nothing new to me there. But here the TYT goes NW through Emigrant Meadow, by Relief Reservoir, and hits highway 108 near Kennedy Meadows (that's the NORTH Kennedy Meadows to anybody familiar with the PCT) then does an 8.5-mile highway walk back east most of the way to Sonora Pass, getting off the highway near St. Mary's Pass. Obviously, it is stupid to walk the highway for 8.5 miles, so the book includes the maps for just taking the PCT from Bond Pass, hitting 108 at Sonora Pass, and walking west maybe a half mile to the St. Mary's Pass trail.
From Highway 108, I unwittingly took part of the TYT by climbing to St. Mary's Pass and bushwhacking down the Clark's Fork of the Stanislaus until the trail starts. I, however, went back up to the PCT after 10 miles or so at Iceberg Meadow via Disaster Creek. The TYT, however, continues down the Clark's Fork via the Clark's Fork road for a couple miles, goes up Arnot Creek and Woods Gulch, down Slaughter Canyon, crosses the North Fork Stanislaus and goes west to Lake Alpine before crossing the Mokelumne River and heading up Summit City Creek and reconnecting with the PCT at Frog Lake just south of Carson Pass. This portion gets down to the 6000' range, so it's much lower than the PCT, but I wish I'd known this before I did my hike, because I was just on the PCT from Wolf Creek Pass (where Disaster Creek brought me) across Ebbett's Pass on Hwy 4 all through the Mokelumne Wilderness to Frog Lake/Carson Pass. That's a decent stretch of trail in terms of cool volcanic knobs, but I always prefer seeing new stuff, even if it was a bunch longer and lower. Oh well.
From Frog Lake/Carson Pass the next 35 miles of the TYT are the PCT--over Echo Summit, through Desolation Wilderness to Phipps Peak, where the last 9 miles of the TYT diverge from the PCT to go NE over Phipps Pass, by Rubicon, Stony Ridge, and Shadow Lakes, and down Meeks Creek to Meeks Bay.
So anyway, that's the TYT. A stupid and avoidable roadwalk along hwy 108, one small cross-country section that I happened to do because my old map incorrectly showed a trail there, and further west and lower than the PCT through the Mokelumne. It seems likely (if not obvious) that the non-PCT portions aren't maintained as well as the PCT, but I'd guess it's a pretty good alternate route for anybody that's already done the PCT.