I'm using an Arduino Uno. "Regular" serial is plugged into my computer, and I can receive just fine.

I'm using AltSoftSerial (tried SoftwareSerial, same results) with RX and TX on pins 8 and 9 to interface with a BR-355S4 GPS module. According to the data sheet on that module, the RX and TX are at 5v, which I believe is what the Arduino expects.

I combined the Serial and SoftwareSerial examples to test the connectivity from the Arduino to my PC and from the GPS to the arduino.

#include <AltSoftSerial.h>
AltSoftSerial altSerial;
void setup() {
 //Initialize serial and wait for port to open:
 Serial.begin(19200);
 while (!Serial) {
 ; // wait for serial port to connect. Needed for native USB port only
 }
 printAsciiTable();
 altSerial.begin(4800);
}
void printAsciiTable(){
 Serial.println("ASCII Table ~ Character Map");
 int thisByte;
 for(thisByte = 33; thisByte < 127; thisByte++){
 Serial.write(thisByte);
 Serial.print(", dec: ");
 Serial.print(thisByte);
 Serial.print(", hex: ");
 Serial.print(thisByte, HEX);
 Serial.print(", oct: ");
 Serial.print(thisByte, OCT);
 Serial.print(", bin: ");
 Serial.println(thisByte, BIN);
 }
 Serial.println("~~Done with ASCII Table~~");
}
void loop() {
 char c;
 if(altSerial.available()){
 c = altSerial.read();
 Serial.print(c);
 }
}

The data coming into the Serial Monitor tool looks fine until it starts pulling from the GPS serial stream (ellipses added by me):

...
|, dec: 124, hex: 7C, oct: 174, bin: 1111100
}, dec: 125, hex: 7D, oct: 175, bin: 1111101
~, dec: 126, hex: 7E, oct: 176, bin: 1111110
~~Done with ASCII Table~~
4TM5f3y=›ùÙ)É9Ó¦ÌTM¦ ...

I would like to receive the correct NMEA strings from the GPS module on altSerial and push them out to Serial. The garbled nature of the serial data looks like a baud rate issue, but I've tried a handful of combinations for Serial and altSerial speed with no success. Any ideas?