Yes, we do NOT teach the same gospel. Do you teach that Jesus died for ALL men as non-Cals and Arminians do? Or do you teach that Jesus only died for some men (Limited Atonement)?
When Paul preached, he told sinners that Jesus died for OUR sins. A 5 point Calvinist can never tell anyone this, because you believe Jesus only died for the elect, and you do not know who the elect are. You do not even know if you are elect truth be told.
1 Cor 15:1 Moreover, brethren, I declare unto you the gospel which I preached unto you, which also ye have received, and wherein ye stand;
2 By which also ye are saved, if ye keep in memory what I preached unto you, unless ye have believed in vain.
3 For I delivered unto you first of all that which I also received, how that Christ died for our sins according to the scriptures;
4 And that he was buried, and that he rose again the third day according to the scriptures:
You will probably argue that Paul is speaking to Christians only here, and that is correct, but he did not know these persons were elect when he preached to them, yet he told them Jesus died for OUR sins.
So, Calvinists who believe in Limited Atonement DO NOT preach the same gospel as non-Cals and Arminians, we preach that Jesus died for ALL men.