Trump released a tax proposal last September that included broad tax breaks for businesses and households. He proposed reducing the highest income tax rate to 25 per cent from the current 39.6 per cent rate.
Pressed on the contradiction between his latest comments on taxes and the September tax plan, Trump said he viewed his original proposal as "a concept" and that he expected it would be changed following negotiations with Congress.
"By the time it gets negotiated, it's going to be a different plan," Trump told ABC. He emphasised in separate interviews with ABC and NBC that his priorities were lowering taxes on the middle class and businesses.
Meanwhile, Trump yesterday issued an implied threat against the party's congressional leader for not supporting him as its nominee.
Trump refused to rule out punishing Paul Ryan, speaker of the US House of Representatives, by unseating him as chairman of this year's Republican national convention in Cleveland, where Trump is expected to be officially anointed. He said he had been "blindsided" by Ryan's refusal to endorse him.
"Three weeks ago, he called me and he was supportive - it was amazing. I never thought a thing like this [would happen]," Trump said.
Ryan became the latest in a series of party heavyweights to come out against Trump's candidacy last week when he was said he was "not ready" to support him, although talks between the pair are continuing.
A more explicit threat came from Sarah Palin, a former Republican vice-presidential candidate and Trump's most high-profile backer in the party, who said Ryan's stance would cost him his seat in his home state of Wisconsin, where he is being challenged by a pro-Trump candidate.