I think that Congress did surrender a lot of its war making authority to LBJ during this time, although at the time they passed the Tonkin Gulf Resolution, they may not have realized how much. No one could have foreseen (well, they couldhave if they studied their history) how long the Vietnam War was going to drag on. LBJ was famous for bullying members of Congress and people in his own cabinet when they spoke of withdrawal or decreasing funding for the war. LBJ wanted a free hand in how he ran the conflict, and for the most part, Congress gave it to him.
As brilliant as the Founders were in establishing how the government was supposed to work, the United States is not immune to history. The sad fact is that democracies devolve into empires -- if Greece and Rome and Britain were are sufficient examples, simply by those in power stealing more power for themselves. For the United States, the consolidation of power, along with the destruction of checks and balances that occurred during wartime was not new to Vietnam; Korea even earlier began this process and the current Gulf Conflicts continue it. By Constitutional standards, Congress, not the president, can declare war. The Executive Branch has far exceeded its original intent.
I don't agree that the Gulf of Tonkin Resolution was an instance of the Congress giving up its control over the executive. Congress would have given up control just as much if it had declared war the way the Constitution says it is supposed to.
I do think that Vietnam gave the executive more power because all wars give the executive more power. The people look to the executive for strong leadership in times of war and give the executive more leeway in those times. Vietnam was unique to that point because it was such a long war. This meant that the executive got the "benefit" fo these extra powers that are informally granted in time of war for a very long time. This helped to consolidate power to the extent that political scientists of the time referred to the "imperial presidency."