Found the book I remembered on Amazon. The blurp reads:

"From tearing roads through the jungle to blasting out Viet Cong positions, from convoy escort to rescue operations, the tank crews in Vietnam did it all. Here is the best account ever of this fascinating aspect of the Vietnam War: Sgt. Ralph "Zippo" Zumbro's evocative, action-packed memoir of a year with A Company, 1st Battalion, 69th Armor.

Always bold, sometimes reckless, the "tread heads" who manned "The Ape," "Assassin," and "The A-Go-Go" devised new combat tactics -- often in the heat of battle. Cut off from supply lines, they became master jury riggers and scroungers. They shared a unique perspective of Vietnam: from smiling Coca-Cola girls who betrayed you to Charlie, to buddies who stayed above the hatch a moment too long -- and took an anti-tank rocket in the chest; from impromptu fish fries to the Tet Offensive. When Sgt. Zumbro's tour of duty ended in June 1968, A Company was the most highly decorated unit in Vietnam."

One of the bits I remember best was how - on the morning that the Tet Offensive started - several tanks from the unit had been detailed to "familiarize" some newly-assigned, high-ranking staff officers with the current area of operations. Essentially, the unit was conducting ride-alongs, with these individuals occupying each tank's (generally empty due to understrength manning) loader's seat. When the excrement hit the rotary air impeller, these "ride-along" tanks found themselves with colonels and even *generals* serving - quite happily IIRC - as loaders for the first few hours of the battle, until the officers' various assigned units tracked them down and retrieved them.