I worked as a NY PI attorney for a decade. In my experience, very few cases go to trial. The reason is juries are fickle and nothing is guaranteed. A bird in the hand is worth two in the bush. This works both ways.
If your case is legit worth two million (and most of my former clients always thought their cases were worth much more than reality), then there's a reason the railroad is not offering a higher amount. It could be your attorney is clueless and making unreasonable demands, or they simply will offer up more on the court house steps. It's super hard to tell. Also, you probably have soft tissues injuries, and these are notoriously difficult proving. Even if your doctor is sure, what are their doctors saying? What's in the IMEs? It's completely possible their jury verdict review (and they have one, it will summarize all jury verdicts with facts similar), suggests the case is not worth millions or they could get a very low verdict.
Past that, there's nothing wrong with going to a second attorney. Let me tell you about a few possible issues though (key word is possible), and this is only so you are mentally prepared.
One possible problem is getting the prospective new hire attorney all the information about your case this late. Your case is probably under Federal law? I'm not sure how, or if, the federal law details what to do specifically. In many states, believe it or not, your attorney is legally allowed to charge copy fees for medicals, correspondence and pleadings (in NY at least I think it's .25 per page). Does your current attorney have other out of pocket expenses? Did they pay for expert testimony? Investigators? You might find your attorney reluctant to hand over some stuff they paid for, and the law might support them here too. Some attorneys will hand this stuff over willingly. They may know they are in over their head, or their relationship with you is affecting the case. Either or, it's going to be hard for a second attorney to evaluate your case without this information. You may have to switch attorneys, as that's the only way they might get your entire file, and then trust what your second attorney tells you about the case.
I can tell you flat out too, there are red flags about your case and concern. An attorney who has a case worth millions generally will communicate with you often. The attorney stands to make decent money (no idea what the fee cap is with railroads or how the contingency fees are set). Not all attorneys, some are clueless. That said, clients are people, and people often say stuff based on what they want. People manipulate. The number one complaint is clients think they should be getting more than their attorney is telling them, and so this can cause rifts. Before you freak, I am simply telling you it's a common problem, not that you are doing this.
One other issue. A new attorney doesn't know you or the case. If your case is getting ready for trial, your current attorney and their office should know you fairly well. They will be aware of all of your medical treatment, and how well you did when talking to them and when being deposed. This matters, as some clients are more jury presentable than others. They will also potentially have spoken to your doctors, investigators, etc. A new attorney can catch up, but they have missed out on the long process. For a time, they will be at a disadvantage.
The last thing, kinda pulling all of this together, if and when you see another attorney be level headed, honest and clear about what your current attorney told you. The new attorney is not going to take on a case, at this late stage where they are only getting 1/2 of the normal fee, if the client is a royal pain in the ass. Remember, you may be asking them to pay your current attorney up front for all of the current case expenses. The potential new hire attorney will know when it comes to the merits of your case, if you are exaggerating.
Set up an appointment, preferably with an attorney outside your area, and go talk to them. There's nothing wrong with calling the attorney who has big ads in the phone book or TV. Those ads are expensive, and there's a reason they can afford them. See what they have to say. Raise the issue about your file with them, or ask them on the phone when you call. Most importantly, remember it's up to them whether they think your case is worth it, and so be calm, honest and listen.