Slow jerky servo response to slider input

//This program allows position control of the servos via RemoteXY client.

#include <Wire.h>
#include <RunningAverage.h>
#include <Servo.h>
#include <SPI.h>                //http://arduino.cc/en/Reference/SPI
#include <Thermocouple.h>         //http://github.com/JChristensen/Thermocouple

//////////////////////////////////////////////
//        RemoteXY include library          //
//////////////////////////////////////////////

// RemoteXY select connection mode and include library 
#define REMOTEXY_MODE__HARDSERIAL

#include <RemoteXY.h>

// RemoteXY connection settings 
#define REMOTEXY_SERIAL Serial
#define REMOTEXY_SERIAL_SPEED 9600


// RemoteXY configurate  
#pragma pack(push, 1)
uint8_t RemoteXY_CONF[] =
  { 255,2,0,24,0,153,0,8,13,0,
  130,1,2,35,96,27,5,67,4,50,
  4,20,5,2,26,6,67,4,50,10,
  20,5,2,26,6,67,4,50,16,20,
  5,2,26,6,67,4,50,22,20,5,
  2,26,6,4,128,68,51,26,6,2,
  26,4,128,3,51,62,6,2,26,129,
  0,9,41,22,6,17,84,104,114,111,
  116,116,108,101,0,129,0,67,42,18,
  6,17,67,104,111,107,101,0,129,0,
  19,4,20,6,17,69,110,103,105,110,
  101,0,129,0,19,10,23,6,17,69,
  120,104,97,117,115,116,0,129,0,19,
  16,28,6,17,87,97,116,101,114,32,
  79,117,116,0,129,0,19,22,23,6,
  17,87,97,116,101,114,32,73,110,0 };
  
// this structure defines all the variables of your control interface 
struct {

    // input variable
  int8_t choke; // =0..100 slider position 
  int8_t throttle; // =0..100 slider position 

    // output variable
  char TempEngine[6];  // string UTF8 end zero 
  char TempExhaust[6];  // string UTF8 end zero 
  char TempWaterOut[6];  // string UTF8 end zero 
  char TempWaterIn[6];  // string UTF8 end zero 

    // other variable
  uint8_t connect_flag;  // =1 if wire connected, else =0 

} RemoteXY;
#pragma pack(pop)

/////////////////////////////////////////////
//           END RemoteXY include          //
///////////////////////////////////////////// 

//MAX6675 SPI pin definitions
#define csTC1 6             //chip select for MAX6675 #1
#define csTC2 7             //chip select for MAX6675 #2
#define csTC3 8             //chip select for MAX6675 #3
//#define csTC4 9             //chip select for MAX6675 #4

//Additionally, connect the MAX6675s as follows:
//MISO  Arduino pin 12          //master in slave out
//SCK   Arduino pin 13          //serial clock

Thermocouple tc_engine = Thermocouple(csTC1);    //instantiate the thermocouple objects
Thermocouple tc_exhaust = Thermocouple(csTC2);
Thermocouple tc_waterin = Thermocouple(csTC3);
//Thermocouple tc_waterout = Thermocouple(csTC4);

float EngineTemp;
float ExhaustTemp;
float WaterInTemp;
float WaterOutTemp;

char EngineTempChar[6];
char ExhaustTempChar[6];
char WaterInTempChar[6];
char WaterOutTempChar[6];

//define Servos
Servo ServoThrottle;
Servo ServoChoke;

//Thermocouple Read Timer
const int read_interval = 500;
unsigned long currentMillis = 0;    // stores the value of millis() in each iteration of loop()
unsigned long previousRead_Millis = 0;

//SETUP--------------------------------------------------------------------------------------------

void setup() 
{
    RemoteXY_Init ();  
    Serial.begin(9600); //initialize Serial
    ServoThrottle.attach(9);
    ServoChoke.attach(10);
    delay (20);
    RemoteXY.throttle = 50;   //sets GUI slider to mid
    RemoteXY.choke = 50;    //sets GUI slider to mid
    }

//LOOP---------------------------------------------------------------------------------------------

void loop()
{
 RemoteXY_Handler (); 
 ServoControl();
 ReadThermo();
 currentMillis = millis();
}

//---------------------------------------------------------------------------------------------  
 void ServoControl()
{
        int ms = RemoteXY.throttle*20+500; 
        ServoThrottle.writeMicroseconds(ms);  
        int ms2 = RemoteXY.choke*20+500; 
        ServoChoke.writeMicroseconds(ms2);  
} 
//---------------------------------------------------------------------------------------------  

void ReadThermo()
{
    if (currentMillis - previousRead_Millis >= read_interval)        //only call when timer runs out
        {
            //read thermocouple temperatures as float
            EngineTemp = tc_engine.readC();
            ExhaustTemp = tc_exhaust.readC();
            WaterInTemp = tc_waterin.readC();
            //WaterOutTemp = tc_waterout.readC();
            
            //send to RemoteXY app
            dtostrf(EngineTemp,3,2,RemoteXY.TempEngine);
            dtostrf(ExhaustTemp,3,2,RemoteXY.TempExhaust);
            dtostrf(WaterInTemp,3,2,RemoteXY.TempWaterIn);
            dtostrf(WaterOutTemp,3,2,RemoteXY.TempWaterOut);
            
            //reset timer
            previousRead_Millis = currentMillis;
        }
}