Which kit did you use? I suggest the employment of  BD SMARTTM RACE

cDNA AmpliWcation Kit (Clontech, Palo Alto, CA, USA).

I suggest u use following things must 

Highy fidelity RT enzyme is Superscript III- Invitrogen and Taq DNA plymerase is Phusion Taq from NEB 

Check with both PCR reaction (outter PCR and inner PCR ) in gradient PCR

check cDNA concentration and use PCR reaction only 100ng - 200ng enough 

I suggest you go for   Invitrogen RECE pcr kit for RECE PCR amlification.It works well.

all the best

Did you try other annealing temperature?

If not, you should change PCR program(annealing or elongation temperature and so on.).