there's no such phrase like 真想让 here in Chinese ,真想 means I really want to.... ，and “让”is more like a causative verb ,,like "let ,have ,make " in english language, it's literally equal to these words above ,but when putting it into practice ,you english speakers may prefer to say : I would like you to do sth. for me,,I don't want you to help me ,,and the like ,and it would be ambiguous putting 我想 and 让 together, for instance, 我想让座（I would like to give up my seat on the bus to someone..）,and 让 in this line can be totally different from that in 我想让你帮我 :)

真想让=I really want (sb. )to do sth.This idea being out of my mind.

你是真想让我……you are really want me to do sth. 看来你是真想让他走哪，那就让他走吧。 我真想让你回答我这个问题，但是你无法回答我。 他真想让她回来，因为他想她了。

wanna sb. do sth.

真想让=want to