I feel "정말로" is stronger impression than "정말". "정말" sounds more natural than "정말로", for a common converstaion.

'정말로' is always an adverb. '정말' is sometimes an adverb, sometimes a noun. 1. 정말 = 정말로 as an adverb 정말 힘들었어요 = 정말로 힘들었어요. 2. 정말 = (being true of someone's saying) as a noun. 정말입니다. 믿어주세요. = What i'm saying is true. Please believe me.

thank you!!

나는 돈이 정말 필요해 / 정말로 필요해 나는 너를 정말 사랑해 / 정말로 사랑해 이 음식은 정말 최고야 / 정말로 최고야 I don't think there is much difference in it?