Today on my way to work my 1993 ford ranger would shift fine but would refuse to go over 35mph and shook pretty bad. I don't know where to start

 

Welcome to FTE.

I see you don't have any replies yet, so I'll see if I can get things started.

Scan the computer for trouble code clues & post All code Numbers, as they can help focus a trouble shoot.
You have OBD -1 = On Board Diagnostics system 1, so you don't need a scan tool to be able to scan the computer for codes, you can use a paper clip jumper to have the dash CEL blink the codes, or hook up a analog meter, or test light to the under hood DLC = Data Link Connector & have the test light blink the codes, or watch the analog meter needle swing to indicate the codes.
If you don't know how to make the connections, have a look here. Ford ? OBD/OBD2 Trouble Codes

Sounds like you may have more than one problem. If the CEL was lit & flashing when it was acting out, it was indicating the computer had detected a cylinder misfire & set a trouble code clue.
If you also had a fueling problem, say from ice in the fuel line somewhere restricting fuel flow, or a fuel pump, or acting out fuel pressure regulator, a fuel pressure & flow rate test at the under hood fuel rail Schrader valve test port would be a good idea.
On your OBD-1 system, you can use the jumper wire to run the fuel pump without starting the engine, for the pressure & volume tests.

If you come to think it's a ignition problem, raise the hood & have a look at the primary & secondary ignition system parts & wiring, looking for a electrical arcs & sparks break down light show around the spark plugs, plug wires, coil, maybe spritz them after dark with a spray bottle of water at warm idle, to see if you can spot a break down & let us know what you find.

 

We filled it up with gas and it started running fine again I guess it's just cause it's an old truck I can't let it get too low
Is that why? Or is it a sign of other problem

 

How low was the fuel gauge indicating before the refill & it starting again?
Have you had this problem before?

 

It was about a quarter tank but no this is the 1st time anything like that has happened, but I don't understand how filling it up fixed it. I talked to a few people about it and they chalked it down as it just being an old truck.

 

Chalking the problem up to it just being a vintage vehicle isn't a good answer. Things happen for a reason, best to perform some basic trouble shooting to try & determine the root cause & fix it, so you don't have it lay down on you at a bad time that you can't recover from.

I've seen faulty gas caps not properly vent the fuel tank & cause stalls. Next time it does it, pull over, loosen the gas cap to equalize fuel tank pressure & see how it goes. If it immediately recovers, replace the gas cap with a OEM part.

Given the vintage of this vehicle & the possibility of more than one problem, I'd also perform the fuel pressure & flow/volume test & scan the computer for any set, or pending trouble code clues & post the Numbers.
I'd also do the ignition system spray bottle "wet down" test, after dark, at warm idle, to see if you may have any high voltage ignition insulation problems mucking things up.

More thoughts for consideration, let us know what you find.

 

Will do. I'll start with the codes and I'll keep this page updated whenever i find anything out.